3. Even as a filthy casual, I can easily try out a bunch of skill combos
That's by design, and it increases replayability. It may be better for you personally, but it would ruin a lot of people experience if respeccing and rerolling was as easy as is in D3 (just change skills and some gear).
Personally I hope this doesn't change, ever, is the only thing that keeps a lot of people playing for years (and it ahs been detrimental for D3 replayability).
4. No need to trade for critical items as you get showered with loot anyway (I prefer to play self-found)
If you play permanent leagues over time this shouldn't be that much of a problem either. (You should as you say you are super casual.) Except maybe some T1 uniques (Shavrones), but they are not supposed to be easy to get, nothing wrong with that.
5. No awkward periods of grinding when you don't yet have the items/skills/passives your build needs
I agree that character building can be odd in this game, where you do several transitions. In some way is fun, but in other is strange. I'm neutral towards this, but that's because I have adapted after playing a long time probably, can see how this is problematic for new or casual players.
It has been improving though, you can almost level up with any combination now. ES based characters levelling organically (self-found gear in fresh leagues) still is a PITA yet though...