Two things brought up elsewhere that people really should stop and consider right now before running off half-cocked:
1. PSN/XBL patches do not get approved overnight. They typically have 3 - 6 week lead times at best, unless you are a first-party development team and get fast tracked. That means that this adjustment to Sent's health was almost certainly not reactionary. It wasn't because of whining of online players. If anything, it seems more possible in this context that the adjustment was something the team decided on when finalizing balance, but could not adjust files on the gold disc.
People have been demanding X features since day one, but even if the team completed those features within a week of request, it would still take weeks for the patch to be deployed.
2. Adjusting health is probably the simplest, and safest thing, that can be adjusted in the game. It is much more drastic and unwise to casually adjust hit boxes, frame properties, invisible switches like gravity and fall characteristics, and even damage; all these can totally screw up and later a character's style. But health is merely how much you get punished for screwing up and taking a hit - plus how many other characters have a 100% damage combo that is applicable to the affected character.
It has already been pointed out that even with many characters now able to easily get in on Sent, Sent's high health can still be a real drag in the match; because Sent can survive a few stupid screw ups, and many characters have to get in multiple times to kill him off, even if it's not that hard to do.
Of all the changes they could make to the game this early, tweaking Sentinel's health is honesty the most basic and even most obvious; and like stated above, was probably something decided on before the game even hit the shelves. If that's the case, we're only seeing Sentinel the way they intended now, instead of on day 1. Might explain a few things.
Hell, as far as I'm concerned it's a good thing to get this out of the way right now; a lot of people like playing Sentinel not because he's easy or to rack up mindless wins, but because they like the style and tactics (actual tactics, not noob shit). However, there's no denying even if you want to play Sent "correctly" and not lame everything out, you still are enjoying sitting on a nice big damage sponge. Now, there's risk involved to require playing Sentinel well. We'll see how it goes.