To an extent sure, but optimization for a particular type of content, even as a pure DPS class for 2s vs 3s and variations on comps, dungeon spamming, farming, raiding, BGs is not going to happen with only dual spec.
More often than not, for me (as I tend to play tank classes), I’ll often respec to run 5-mans with friends who are tanks, or for PVP, or sometimes when not tanking raids. While dual spec would be pretty convenient sometimes, it wouldn’t solve the respec “problem” for me personally, but it would displace it a little.
Maybe. I mean, I can definitely see how dual spec would fit in. I don’t personally think it solves the problem that you’ve identified as well as either reducing/removing respec fees, or simply allowing free respecs while out of combat. All of that would change the way some people play (which might not be a bad thing - it might even be good).
In any case, as you say, Blizzard is the judge when it comes to what features we do end up getting, and they’ve already introduced changes that (at least in my personal opinion) are much worse than something like dual spec.