People come in here posting they have a 400whp goal because they don't know how fast 400whp really is on an AWD... but even then, anyone who gets to 400whp pretty much has enough experience to handle 400whp... given the fact that they don't take a big plunge into upgrades too quickly.
your theory is that someone with a stock sti, 230whp, will upgrade to 400whp right off the bat, resulting in a big change of driving, which I agree can be dangerous. But who really does that? Who is going to really drop all that money AT ONCE to go from 230whp directly to 400whp? Most likely, they will get upgrades that get about 50-60whp max at once, and drive it for a while, and get a little more power, until they reach their goal. So in my theory they'd be going 230whp... plus a few mods... then be at 260whp... then maybe some other mod and be at 280whp... then 320whp... etc. So they are pretty much taking step by step experience.