dnd 5e – If spiritual weapon allowed you to use spells with it would it be broken? Yes, but if I put this limit on it would it still be?

I am toiling with a spiritual weapon-based subclass homebrew idea. In the base game, the way you would use spiritual weapon would be alongside a cantrip or weapon attack. This is because you can’t use 2 spells in the same turn in the base D&D ruleset.

First to describe it in full: at the third level, you would gain the ability to use a spiritual weapon with other spells with a limit on what spells you could use.

Essentially, the homebrew would be a cleric that could be able to use spells with spiritual weapon. I’ve been doing the numbers comparing it to other clerics and the damage seems strong even if you limit the spell slots usable when attacking with it to using spells up to half the cleric spell slot level you used to cast it rounded up. Only being able to use 5th level spells like flame strike would be the strongest option. At level 20 The damage with a 9th level spiritual weapon and a flame strike would be 4d6 fire damage, 4d6 radiant damage, and 8d8 radiant damage. In total that would be 112 damage assuming you got the highest possible roll. Even at level 20, this is a high amount of damage, especially for a cleric but I don’t think there is a way to increase that. A paladin power gaming super hard can do around 200 damage. Any other cleric can do 70 damage with firestorm. Most spellcasting classes can do 240 damage with meteor storm alone. Of course, this is at extremely high levels.

At low levels, it has reasonably higher damage than most classes but still does less damage than a war cleric or any other character with the Great Weapon Master feat alone. I’m thinking at most levels, except when you get 9th level spells, it should be fine. Clerics don’t really gain higher damaging spells past 5th level so it’s hard making the damage comparable. They gain more utility instead.

I’m thinking if I stray away from stronger subclass spells it should be fine. What do you think? I’m also considering that someone has already thought of and made this idea but I don’t know of any cleric class that does this in homebrew. Of course, it can’t be stronger than the peace domain so it’s probably fine.

Now in hindsight, I realized that a cleric can do more damage with toll the dead and spiritual weapon at level 17. They can in fact do 112 damage exactly. This makes the highest possible damages more comparable but flame strike is an area spell so it can do more overall damage but so can something like sunburst with that logic. It would also consume fewer resources.

I’m essentially asking for any thoughts on if this is too strong. Also, remember that the built-in limit is you can only do this with cleric spells off your cleric spell list. So no divine soul sorcerer tomfoolery.