Adding stuff doesn’t always fix everything: that’s how Blizzard got into this mess in the first place. They knew that levels were going to be a problem going into Cataclysm and MOP (when levels capped at 85 and 90), so I’m pretty sure they’ve been looking for way to fix this that didn’t involve just putting a hard limit at 100 or something. Compressing the leveling process makes the state of leveling more rewarding because it takes just as long to get from 10-50 as it does from 1-120; the time spent leveling wasn’t the issue, it was how much jumping around from expansion to expansion you had to do once you broke past certain thresholds. Expansions became less about questing and story line and just grinding away until it was time to leave. The expansions that were fun when they were current turned into just another hurdle on the way to max level, and that is not fun. It’s also something that they learned from Classic: if every level has a reward, even incremental ones, then the leveling feels better. Compare this to how current leveling goes: after 100, there are no rewards to your character, and it feels like crap because all that really matters is getting to endgame content ASAP.
For example, of how the squish might help your character feel better, the talent progression system is compressed: the current is 15-100, but the talent gain isn’t consistent (every 15 levels until you hit the last tier). If you can compress that from 10-50 or even 1-50, you should be able to shrink the usable talents from 7 tiers to 5 or 6 - something nice every ten levels on top of gaining abilities and improved abilities. This potentially means one of two things: some talents might actually become baseline, and less junk talents. (Admittedly, I didn’t watch the presentation on talents, so I don’t really know how this is going to go; they could be bringing back skill trees, for all I know. That’d be nice.)
Two, as I mentioned before, the leveling process itself is greatly simplified: choose an expansion, and spend as much of your time there as you want. Want to spend 10-50 in Northrend? Go for it. Want to hurt yourself and do it all in Draenor? Knock yourself out. No more jumping around when the levels run out, no more unfinished storylines, no more going to a new expansion being completely undergeared because of scaling issues, just pick a timeline and go with it.
Look, I know it seems like you’re getting weaker because the numbers are smaller, but you’re getting more bang for your buck, numerically speaking.