That's a huge improvement, and it's sad that something so basic and obvious finally dawning on a former 3E and PF designer is even something to celebrate.
But, SKR's views are still woefully...limited.
Rebuilding a character each day is only part of the problem. The ease of resting is only part of the problem.
Even if you give Fighters the ability to pick feats each day, feats fundamentally work differently from spells. Spells are generally distinct items that don't rely upon each other. Of course there's combos, and some spells get a boost if used with certain other spells, but in general this holds true. Feats, on the other hand, have prerequisites. Both requirements aside from sheer character level and more problematically...other feats. Even if a Fighter can rebuild daily, the feat trees ensure he really can't. And feat trees themselves aren't always evil. A lot are, and have "punishment requirement" feats that suck, sure. But, as feats are not like spells, many of them actually DO build upon each other and the tree is justified. Just giving fighters retraining doesn't work, you would need to completely redefine how feats work and what they are.
Another thing is SKR thinks breadth is the only source of power. While versatility is a source of power...the fact is IME casters don't *actually* change that much day to day. That haste spell is godly any day of the week. A wizard would be crazy to not prepare Glitterdust every day they adventure. That save or die will instant win an encounter most days, too (you may change it to focus on a certain save, but usually you'll want SoD's that hit different saves simultaneously prepared anyway). And martials don't have anything nearly as good as these options. I guess as Xykon would say, "Power is power."
Also, the whole "fight all day" thing is a myth. Without unlimited healing, a thing SKR and others at paizo dislike (see the Glorious Heat debacle), a Fighter will often ask to rest long before the casters at mid and high levels...if not low levels, too. Because hp can evaporate so very fast, and the effects of completely running out of hp are a *bit* more harsh than having no spells left...just a bit.
Also, casters can do the fight all day thing better anyway. They get a ton of long duration godly buffs, many of them self-only, and in PF tend to get even limited use stuff like flight or greater invisibility with the option to split up the use as they see fit. Weapon Focus has nothing on that.
Finally, even if resting were hard....and I say this from the perspective of a DM, not a player (as a player I actually push for as many encounters in a day as I can get, I like the rush and I want to help make sure the martials can shine and excessive spell use is actually punished...I act this way regardless of the class I play)
...I don't want to HAVE to have 4+ encounters every fucking day just to keep the classes balanced. That's just goddamned impractical a lot of the time, and guarantees a ton of "filler" encounters only there to pad out the combat rounds in the day that aren't actually fun. Plus, all those encounters each adventuring day means rapid leveling. 13.3 equal CR encounters is a level up. If you're doing 4+ per day, the party's leveling up every four fucking in-game days! That's stupid and un-fucking-sustainable!
And I'm swearing so much because this particular issue especially pisses me off and vexes me as a DM.
AND NO ONE EVER TALKS ABOUT IT (not from this perspective) !!!!
TL;DR: I think SKR is misguided and ultimately wrong. Big shock.