13a OTOH has a LOT of advancement in many different dimensions. It feels crammed into 10 levels, stuffed in really.
It's a different paradigm (I love that word. I'm really sad that so many have seen it abused and come to hate it. It's such a useful word to have!) with regards to what level means.
As an example in D&D, 3rd or 4th level don't
mean very different things. As whole, characters of similar levels have a similar "power meaning" - of course there are key turning points, but those are not that abundant.
In 13th Age, the idea is that each level really means a good deal more... and also less. If you don't use the partial progression, gaining a level is a significant increase in
everything. On the flip side, if you use partial progression, then the level is sort of the bell that rings when you cross the line: you're just one step further than you were, but somehow that step mattered more than the ones before it. In a way, it's sort of a milestone marker; not that important really, but, in a way, essential.
Granted, it may not feel that way to you - and their's precious little to do on a forum to change how you feel about a complex context

- but when I changed my glasses from "
ok, I get about 3 levels' worth of stuff" to "
my character was this, and is now that... ok, these levels are a big deal" it kind of clicked for me.
But then again, I'm not seeing 13th Age as 4e's successor. It's more like Arcana Evolved vs 3e - it's sort of going sideways from the original branch. (But then again, not really, since I consider AE to be the superior game in all ways... hum... I've got work on my analogies...)
Ok, it's like having a developer of 4e get with a friend and develop something that takes mechanics where they like them, shapes them for the kind of game they want to play and, at the time, they were in "4e state of mind" and thus it feels like a lot of 4e went into the system. From my perspective, a good deal of 4e went into the system - it's just that, as many, many polls have shown, 4e is a massive universe and many people see it as many different things. What the developers answered on the poll "what is 4e" isn't what you feel is 4e.
Or something... man... this is way to zen and introspective - I'm out. Need some bro-dude something to balance all this out.