Really?
Isn't it obvious? Druid spells and abilities offer little or no synergy with this playstyle (apart from shillelagh, which other classes can pick up).
Closest comparison would be a nature cleric.
Tortle with shillelagh and shield has an AC of 19. The nature cleric in full plate with shillelagh and shield has AC 20 and can benefit from magic armour, so that's a clear win for the cleric, apart from at low level when they might not be able to afford full plate.
Both can burn a feat to pick up Booming Blade, but if they don't then Divine Strike puts the cleric ahead at level 8. Otherwise it's a dead heat. Edit: A variant half elf cleric can get Booming Blade free and not miss out on +1 wis.
Spells are similar, but I would say spells like Shield of Faith and Shield Guardians put the cleric ahead as a front liner. The Tortle druid can use Shell Defence whilst Conjured Animals do the fighting, but that is little more than a gimmick.
Wildshape gives zero combat benefit - you can't use it at the same time.
Maybe you and I have different standards of balance. I don't think any full caster should ave an AC over 16-17 without magic items, i just doesn't balance well. Furthermore, of course that' bvious, but it's also not really what I was talking about. But, if our standards of balance misalign to such an extent, I suppose we'll have to agree to disagree.