My monk is still in normal, so I don't know that much about later on. I thought crippling wave with a staff backed by 7-sided and tempest rush felt very different from shock punch with teleport while dual-wielding, the charge attack, and bell glyphed to nova.
I do know my barb can dual-wield with bash/instigate or frenzy/sidearm, pair either with whirlwind/blood funnel and battle rage, or use the sprint/run like the wind build, or put on a shield and use bash/instigate or bash/punish and seismic slam... or use a 2H and go for cleave and leap/iron impact... all of those work, and they all feel very different, handle different areas and different packs in different ways. I can play what I feel like playing, right now, no fuss.
For that matter,
Here are some skill/rune unlock progression charts. Unlocks don't really slow down through progression, and on both the characters I play, runes have very different effects than just art swaps.
Imagining arcane/waller/firechains/vortex isn't the same as trying to kill one in a cave level.
(I assume the skills has been balanced by now, considering all the nerfs i heard about.)
Sure, I got new skills and runes, but rather going "ooh a new skill" I was more along the lines of "Ooh, I can finally remove this placeholder skill".
Some runes were skill defining and using the skill before you had the rune was just not worth it.
I'd describe D2's frostbolt/glacial spike as exactly this. GS is frostbolt, except better in every way. Firebolt/fireball are the same way. Druids' wolves and dire wolves are the same way. Necro golems are the same, except using the lower ones can actually hurt you if you don't know what you're doing. Instead of making the lower ones worthwhile... synergies "fixed" it.
The skill-defining runes aren't like that for all of them. A handful per class are still mandatory, but I can think of quite a few runes that are defined by whatever else you use them with.
Really though. The skill progression in D2 & D3 is basically the same, except D3 is handholding you all the way and keeps the good stuff away from you much longer.
I'd rather get the skills I want earlier and improve on them than using substitutes.
D2 had synergies to handhold you into the proper build, and once you were done with normal you were done with your build. I guess I don't enjoy clicking a + button to add a few %age points as much as the next guy. I'm also using the explosive cleave rune in A2 inferno and it works fine. You get that one before level 12.
What is the current method of powerleveling in D3?
There used to be some nonsense where players would group up and then leave the game before turning in a boss kill so you could get quest XP 4 times, or something like that. That was removed. I'm not aware of a replacement method at the moment.