I am pretty sure you will be able to see my point that characters with 21+ AC EVERY combat round are "too indistructible" (add in Haste and we are at AC 23). And thanks to mage armor the fighter NEVER will have more AC, actually never even the same. The fighter will have AC 18 or 20 (1H or 2H, and as 1H+Shield is boring to play probably AC 18). With the Spell Slots it is still playable, but with the Spellpoints - unless they have some special rule to prevent problems here, even I - who likes to use the Shield spell myselves ^^ - sees problems here.
The Paladin at my table has an AC of 21 at level 7. Before the player moved away, our War Cleric had an AC of 21 at level 3. It doesn't break the game. They are not too indestructible. They get hit less than others, but the majority of creatures hit them at least 25% of the time, and that is not accounting for save vs. spells. Our paladin almost died after taking a good fireball near the end of an adventuring day.