You are again ignoring system differences & all the ways 5e has overly simplified, choosing one feat over some other feat was a meaningful cost because there were so many great feats. A spellcaster absolutely
could take feats like that but unless they needed those for a prereq to some other feat or PrC it was quite the opportunity cost to eat with
questionable returns or
value. Making a case for the caster who specializes to do that one thing ignores all the other things the caster gave up the ability to specialize in. Unsurprisingly 5e's quest for simplicity snapped off both of those options
That depends entirely on what part of the game's life cycle you are in and what books are allotted to you. A Human Wizard gets 2 feats at first level, and you get them every 3 levels, plus bonus Wizard feats every 5. There aren't many choice Wizard feats that you can't get with that; without metamagic reducers, it comes down to spell focus and item creation, and even then, not all of those are worth talking about (Craft Staff for example, is a huge waste of time).
That's the game as it was originally designed, so spending an early feat on a skill focus to increase your survivability is not a big deal. What else were you going to take? Dodge? A case might be made for Improved Initiative, but I digress.
Add more books? Well now you have Steady Concentration so you can take 10 on those checks.
I understand that different tables played the game differently, and if you're trying to qualify for your Dweomerkeeper/Incantatrix with Initiate of Mystra, feats are in high demand, but by that point, you can make custom items that grant a +10 competence bonus to skill checks (say, Concentration) for 5000 gp (since you made it yourself), though that's likely overkill, and the vastly cheaper +5 for 1250 gp is a steal.
So no, I'm not ignoring system differences; if you wanted to make not having to worry about losing spells happen in 3e, you totally could and it wasn't difficult to do,
by the rules presented, nor were the sacrifices really that big of a deal. Like say, playing a human. Vs. what? No PHB races had caster stat bonuses, Elf costs you hit points, and so the only serious contender for Human is maybe Dwarf. OTOH, if your table is allowing Lesser Aasimar or LA buy off for your anthropomorphic bat Druid, then yeah, maybe that is an issue, but when you're playing the game at that level, as I said, there are plenty of other options to look at.
And as for readying an attack? That's your standard action. Most everything has multiple attacks per turn, so it's far better to just attack and try to stop the spellcaster the old fashioned way. By reducing hit points to zero.