[Rules Question] Do you allow Summon Greater Demon ?

As mentionned in the title, with the release of the monster manual and the clear buffs of many demons and other monsters, I am concerned about allowing the Summon Greater Demon spell.

Currently, every spells in the 2024 Player's Handbook that summons or conjures a monster provides a template for the monster and does not allow players to summon creatures from the Monster Manual. Summon Greater Demon is a Xanathar spell and therefor was not converted.

My issue is the Barlgura, for example, can now cast a 6th-level Phantasmal Killer. Yes, I know the spell is sub-optimal, but it still means that a level 4 spell allows you to have a super strong monster who can cast a spell higher than the spellslot used to summon him. It appears to me that this spell in the new system clearly goes against the currently intended meta for these types of spells.

I am heavily leaning on banning the spell at my tables until it is reworked. Thoughts ?