Paragon tier puts 5e more into superhero territory. If the old and decrepit wizard isn't actually an angel, is he about as good as resisting being knocked over (+6) than Arnie the 22 year old weightlifter (+5 on a 1st level character barb). It might be a good idea but I doubt it. There are already a bunch of ways to boost saves (monk, Paladin, artificer, various spells, Resilient, Indomitable, Bardic Inspiration, etc.) and it is hard to land even DC 20 spells on my 19th level players with any reliability.
In my big battle against Irenicus in the Abyss, my BG2 campaign had the following spell levels cast (including the BBEG and 4 Glabrezus, plus an Arcane Trickster, 17th level cleric & sorcerer) in 5.5 rounds of combat:
9: 2
8: 3
7: 2
6: 4
5: 5
4: 1
3: 6
1: 2
Cantrip: 11
Some of the lower-level slots were Glabrezu innates, but that's still 14 spells of 5th level or below and 11 of 6th level or higher... plus a lot of cantrip uses. Only 5 of the cantrips were the Rogue doing Booming Blade. The others were by either Irenicus or the players... probably Sorcerer Quickened cantrips.
They are up to level 19 now and cantrips are used quite frequently.
Every time I've played a wizard (even at 10th level) I have felt like I have the wrong spells prepared for the situation. Cutting down my choices to an even smaller amount takes away from wizard. If I want a small number of choices I'll play sorcerer or warlock or artificer or ranger.
The 1-minute swapout partly patches this, except no other character is going to need a 1 minute break. It might be better to make it cost a full-round action (if such a thing can be added). That way a wizard can swap mid-combat, but only by doing nothing for a round.