I had wondered why you kept referring to the arena as a "Corporate Branch Office", and now that I've seen your explanation here I can tell why. I entered it, and thus began this situation, by referring to it as the Headquarters, and had named it as such in my original post. Then, on your own volition, you arbitrarily decided that this wasn't the Headquarters, and that this was just some random corporate branch office.
I do apologize for not trying to discuss this with you earlier. I am very interested in dynamic stories written by the seat of my pants, so to speak, and feel that planning out a storyline beforehand really cheapens the feel of freeform roleplaying. I didn't think that you'd get so upset at my character attacking your faction's HQ as to outright retcon Gene's workplace, and so confidently went ahead with my idea for a story hook.

Corporate offices don't use concrete blocks for their flooring. Nobody does. It's difficult to bring in and replace, wears down quickly compared to most tile floors, and most importantly looks hideous. Nobody in their right mind would use concrete for their lobby flooring. They might do it for warehouses and hangars, but certainly not for places humans are meant to be in. Gilgamesh would "bother lining it with corporate niceties" because not making a workplace completely disgusting to look at is one of the most basic tenets of workplace design, architecture, and human nature. Nobody likes to go to work every day by walking into a fugly lobby that went out of its way to use inferior and more inefficient flooring.

I had assumed that, like any corporate office, the Gilgamesh office branch headquarters used tile or carpet flooring for its lobby. Thus, the thought of using the floor to form a shield that not even Demon Arm bullets and acid could destroy hadn't crossed my mind. I'll talk about what our characters could have done later.

The idea of Gilgamesh solely using its private army for all security matters is completely insane. Do the Reclaimers work at the warehouses and office complexes in full BDU, wielding their Demon Arms and assault rifles? How does Gilgamesh Inc. manage to fund all this? Keeping dozens of heavily-armored, specially-trained soldiers deployed at dozens of locations at a time is a feat for most countries' militaries, let alone a moderately-sized PMC. You don't need supersoldiers to deal with every security concern.

Contracting with a mundane security firm would cover almost all of the same stuff the Reclaimers would deal with, only it would be objectively cheaper and more efficient. A simple security guard with plain clothes and maybe a flashlight to manage the front desk, and a night shift of several equally-equipped guards is more than enough defence for any office. The precise reason why my first post included more heavily-armed guards manning the second security post is because this was Gilgamesh's headquarters when they needed to be secure. After all, a meeting was going to be held that day.

I fully understand you intended the Reclaimers to be cool badasses. However, you set about proving that in a way that very seriously damaged their chances of being taken seriously.

Firstly, you had them act as first-responders to the threat Gene and Antonio posted. This is a bad thing for proving your badass soldiers' badassery. Threat escalation and the corresponding gradual increase in mook competence is a vital part of demonstrating your characters' powers. If you had started with basic rent-a-cops, ones that would logically be closest to the ground floor, the situation would have had some upward movement when the Reclaimers busted in. This isn't video gamey bullshit, mind: this is something all media ever does. It's a fundamental part of a strong narrative.

Secondly, you had the Reclaimers come in force. A big part of proving a faction's threat is their numbers. Contrary to what one might think, the fewer combatants one fights against, the more likely they are to be taken seriously. This is the Inverse Ninja Law: one ninja has exponentially more impact on a situation than ten. If you had brought in only one or two Reclaimers, we would have much more opportunity to worry about him. Placing eight in the room, however, just lead us to disregard the less interesting ones and, thus, treat them like meaningless cannon fodder compared to their more unique brethren. It's situations like that that prove why the Inverse Ninja Law is a vital consideration when writing a group battle. Two on twos are cool duels. Two on ones are dramatic. Two on eights are just another generic fight between the Cool Two Guys We Can Focus On and the Eight Guys We Really Can't Focus On.

Lastly, your single greatest mistake when trying to prove the Reclaimers as badass is to use generic Reclaimers at all. Since you intended the Reclaimers to be on tier with player characters, you should have had each of your Reclaimers present actually be like player characters. Nameless soldiers, whose only differentiating traits are what weapons they use, are flipping awful for mimicking players, because that's bad character design. A strong character has a personality, a name, a background, and a combat gimmick. What you provided for six out of the eight soldiers in this situation is only a weapon for five of them and a combat gimmick for the last one (Mister Stonewall).

If you wanted to make us interested with the Reclaimers in the lobby, you could have used some very simple writing strategies that have been put into use across the history of writing. First: have a lead up to your special soldiers, to make sure that your audience understands the stakes. Second: field only a few of your special soldiers, to keep them special. Third: field only the special soldiers you've actually fleshed out, so that we understand something about them beyond what weapon they use.

I'm going to briefly touch upon how you made the decision to field a bunch of mooks you intend to be as powerful as the average player character: don't. In any setting, player characters are meant to be special. There's only a few of them, and they're controlled by your audience. You can have characters who are as powerful as or stronger than player characters, but fielding an army of them and wanting to have that army actually do things is inherently destructive to player autonomy. In the interest of keeping conflicts interesting, fair, and fun, you should always endeavor to bring out a force exactly as powerful as the force the players bring out.

A fight between two players and eight player-tier soldiers can only end in two ways: either the players job to them, and their experience is ruined (which you as a storyteller should avoid), or they job to the players, and their intimidation factor is drastically reduced. Either way, it's a bad move that you could have avoided.

I'm not going to say that IncredibleBee is in the right here. He's written a post that contradicts what has been shown previously, and that's why we're complaining. However, both you and him have acted extremely poorly. You, in trying not to have your plot derailed, have shifted reality and lashed out with an army of overpowered soldiers. IncredibleBee, in trying to rescue himself from that army, has powergamed. Both of you have argued bitterly, but to place the blame solely on IncredibleBee would be to outright encourage further behavior like you've demonstrated.

What I want @IncredibleBee to do is edit his post and fix what he got wrong. What I want @Lugubrious to do is take my criticism to heart and use it to improve his writing. Communicate with the players better, don't create situations that have exactly one (nonsensical) solution when the players do something you dislike, and always remember that you, as a GM, should work with the players, not around them. Arguments and retcons only lead to bitterness and poor writing.