Its not a big deal, as long as you have the same number of spell slots... the cleric 11/wizard1 example is just a little better theurg, but its just marginally... the limiting factor is still spell slots, doesnt matter that you have a billion variations of spells, your still limited to how many you can cast... and it dosent make much of a diffrence heal wise or damage wise... as a level 1 cure wounds spell is dependent on character level, so even in pnp 5e that 11wizard / 1 cleric would get be able to cast more powerfull heals...
Secondly clerics by themself have plenty of spells that is more or less a "fireball", and in manycases they can have fire ball by taking the right domains...so as stated a 11cleric / 1wizard in larian can cast a fireball, so can a level 12 cleric of light domain... and even if they dont they have spells that more or less do the same, pillar of flame, blade barrier etc so fourth...
Sure it is nice and fun to have the flexibility of a Teurgh, but its far from as powefull as some think, since as stated, you wunt get more spell slots... and thats it at the core, there is far more powerfull multiclasses as they actually do get more attacks, more damage, etc...
The irony is, the 11Cleric / 1 wizard, loose out on one feat... and they have two main caster stats Int and Wiz...
It's not about power as much as it is about flavor and class identity. If Clerics start dipping Wizard for Shield, Mirror Image and Fireball, Light Clerics lose their unique abilities almost as much as Wizards and Sorcerers.
It's a step towards a classless system where you just mix and match abilities as you please. A system that Larian prefers for their own ip. A system that doesn't feel like anything.