Ultimately, they have not actually answered Ibrahim's question, either - they asked how they used the abilities of their party members intelligently to best the fight. None of THESE solutions have anything to do with using your actual party or their class abilities.... it's almost all external stuff that could be just as easily activated by moderately well-trained dog (#CompanionScratch):
I must have missed it when he provided me his party and class composition, could you link that information for me? make sure it contains his loadout plus available abilities.
1) Get other people to fight for you, you might get lucky!
2) Get other things to do damage for you, there's lots of them!
3) Use the maguffin that was conveniently designed for this fight!
4) Get another monster to fight for you, then kill it afterwards!
5) Get other monsters to fight for you!
6) Stockpile strong items (and explosives!) to use for this fight - like you know it's coming!
7) Get other monsters to fight for you!
NONE of those have anything to do with using your actual party and their actual class abilities strategically or intelligently.
If more than half of your suggestions involve getting other, stronger monsters to fight on your behalf, that rather sounds like a resounding admission that the fight is, in fact, overtuned.
I categorically reject that D&D isn't about utilizing your surroundings to defeat the enemy. I'd also like to point out that the Spectator Fight is OPTIONAL. You can completely avoid that entire area. In fact MOST combat in the game is avoidable.
The overwhelming wrong assumption here is that you HAVE to fight this Spectator. This is the same person who insisted, despite all evidence to the contrary, that you HAD to fight the Duegar - and this was pointed out to them multiple times, by multiple people.
Even if you trigger the fight you can RUN AWAY.
I reject the idea that you don't have options in this game. I reject that using your environment, or running away, or avoiding encounters through dialogue are not CORE parts of D&D. Descent to Avernus, the actual D&D module that precedes these events has examples of ALL of that. There are mobs that will kill you that you need to run away from, there are evil creatures you have to make deals with or have good dialogue checks with, there are things in your environment you have to notice that will help you.
And using potions and buffs during combat isn't metagaming, you are just utilizing resources and being prepared. if you are going to poke around in a clearly dangerous place its reasonable to assume you should be prepared right?
and listen if you want Solasta then play Solasta, its a great game. It has its own limitations though.