Think about this. Let's say you cheated on the Mage tree and gave yourself summon1, prodigy 1 & 2. Now you level up, you can go necromany for a tactical summon, you can get the ice elemental for a strategic summon, you can go evoker to increase your damage, or, let's pretend prodigy 1-3 are where Prodigy 3 is and it is one huge increase to spell mastery (maybe a spell thrown in too), which moves on to the turn-reduction trait. You level up and ALL your choices have an impact on the gameplay. That is fun everywhere.
The problem as it stands are dud levelups. Chains of passive bonuses that you can't see impact gameplay, chains that are prerequisites for what you want, chains that move on to other chains. These are barrier levelups, throttling the thrill of leveling up. They are filler. Topping out at 10-12 instead of level 20, if each levelup was something in and of itself to look forward to, is far superior to watering down the experience of seeing the levelup screen.
I know this is a strategy game, but why not have an ambitious levelup system that is all fun no-filler? Try to be on par with RPGs, not just outshine TBS games. It does not detract from the strategy aspect, it is pure win with no downside. Try to lure in the millions of RPG fans looking for novelty.
One of the weaknesses of the current system is that it doesn't take advantage of the psychology of memory. Memory is the strongest at the very highest and lowest and the finish of an experience. Dud levelups weaken the anticipation of leveling in general, which brings down the experience of the whole system. By spreading out the bonuses in chains of traits, the highs are not as high as they could be. The feeling at the end of the game/session will be the emotional mark of how it ends**. Regardless of what went on, when a person tells you what playing the game is like, they will be recalling the peak(s, maybe in a long experience) and the low point and the ending more than anything else. They may tell a story to justify it, but those emotional points will be what they are justifying. That is reality, as borne out by psychological study (which I base on reading Daniel Kahneman's Thinking, Fast and Slow, other psychology books, and listening to my girlfriend who is in grad school for psychology).
The more robust the fun people are having throughout (and fun leveling fattens this enjoyment gamelong, as they always anticipate the very next levelup which changes gameplay), the less they are sticking on bug/balance niggles and not enjoying how awesome this game brings many systems together. If the next levelup (or two or three) is filler, the RPG aspect is no longer contributing to fun, and the dry patch changes impressions of the whole system.
What about balance? If there were fewer levelups, then bonuses could be combined to always have gameplay effects. Maybe we need fewer melee classes. More is not better in trait trees, because the point of RPG elements is to make your game more fun, if you spread too thin, you will have thin patches of fun. I believe whatever it takes, make leveling up a thick experience where each time that XP bar fills (even if it is less often), that levelup screen means a coveted reward is at hand every time.
** I wanted to steer clear of it in this post, but it may be affected by XP splitting and champs which sit in cities. The experience of champions which you don't use diminish the experience of getting champions. The same dilution effect occurs with champions in my opinion.
