How about matching the animation to the mining rate to fix the mismatch between animation and mining speed? The historic (and current) mining speed seems reasonable for the game, nerfing mining speed just to make the animation match was a cop out solution to the problem.
As for variable durability cost to tools based on target block? Yeah it's more realistic, but at what point do we admit that this is a game and there are going to be unrealistic elements to maintain the FUN FACTOR. Otherwise, we'll just demand more and more realism until we have a reality simulator that is nothing but UNfun. If the devs wanted this kind of meta to the game it should have been introduced much earlier, as it is a fundamental aspect to a MAJOR part of the game - resource acquisition and tool wear. As you mentioned, to introduce it now would be difficult.
Both options, should the devs have their hearts dead set on implementation, would best be done in increments. Maybe tweak the mining speed by 5% per release until the target 20% is achieved. Same with adjusting wear factor to tools. Make incremental changes over multiple releases until the target is reached. Yes, I was one that put up a stink about the mining speed, mostly because of such a large increase in resource acquisition it would constitute. If Tyron had introduced a 5% increase to mining speed I don't think I'd have even made comment on it. The biggest beef I had with that tweak was that it was fix an animation problem (as stated in the patch notes), not to fix a mining speed problem.