Yeah, I'd honestly have to go with Melon here...
His sword is long enough that he wouldn't even have to hold his arm out at this range, and even if he were, it wouldn't be particularly near the hoplon. Unless he was doing something crazy like raising the sword all the way over his head (which wasn't the impression I was getting), it'd be difficult to stop initially. On top of this, Sigurd is stepping forwards with the blow, adding momentum and making it more difficult to stop with the shield. Of course, even with this, the pivot combined with the shield getting in the way would be enough to get her arm out of his blade's path... except her arm has a massive freaking spear in tow, and is trying to maneuver it. Sigurd's arm would likely end up glancing off the shield, but even if it did, it would still be able to swing down far enough to get that long blade down on her forearm. I actually took the time to act out both sides of this as carefully as I could, and from what I can tell the shield hitting the arm as described simply wouldn't hinder its swing enough. Not sure it'd straight-up chop her arm off, since it'd be hard to get the angle of the blade right while practically everything involved is moving, but it'd definitely get through and do some damage, all things considered.
As for the sweep... at first, I was wondering what the issue was, since it seemed like a pretty simple move. On the other hand, upon reviewing Iolanthe's character profile, it's clear what the problem is. Hyperion is a big, long, and likely quite heavy weapon, and using it to make quick slashes at the legs is definitely not an easy feat... it's possible, yes, based on the positioning, to get it under the shield and make a quick strike at the leg, but to do that you'd need to literally drag its point across the ground, and then getting it up to the freaking thigh after that is... I guess it's possible, considering Iolanthe knows her weapon well, but it'd be carrying too little momentum by the time it made contact to really do much. Might cut in a little, and it'd certainly hurt because of the heat, but Sigurd wouldn't be getting much more than a graze/burn from that.
That make sense to you both?