The T doesn't stand for tier, it stands for type iirc. T1 is turnbased (i.e. what is done here, on forums), T2 is speed, which utilizes chats and is done in real time, rather than by way of taking turns.
Neither is better or worse, they're just different styles. I'm not sure where the T1-T5 thing comes from, but I'm fairly sure that it's a misinterpretation. T1 and T2 are simply different approaches to roleplaying combat (one being turn-based, the other being "realtime"), and within them are various methodologies and so on. The reason I say it's a misinterpretation is because T1 - or, for example, your second scale, with T5 - is not defined by quantity of writing. A post can be ten paragraphs and be terrible, or it can be one and be fine. There's no maximum limit, nor minimum requirement, and length is not a dictating factor of talent, quality, skill, etc. I've never seen - even among the most competitive T1ers and T2ers - any concrete references to T4, T5, or really anything beyond T1 and T2. T3 has been mentioned off-handedly, but it seems to just be a substyle within T2.
I'd suggest having a mod move this to the Arena OOC subforum - someone like Skallagrim would have more information on hand to help sort things out.
EDIT:: For this site, the only relevant category is T1; turnbased combat. There may be some people who do T2, but since this is a play-by-post forum it is suited for moreso for turnbased players.