Seeing the way A5E changed some oft-cited overpowered spells (making the 8d6 fireball a rarer version of the spell, counterspell allowing you to salvage your action by casting a lower level spell etc.), I think 5E splat spells can either be made into spells with only rare versions (so getting them is treated like getting a unique treasure), or it could be nerfed as needed. I haven't had personal experience porting over such spells, but I think even if you ported the O5E spell directly I doubt it'd completely ruin the game.One of the players at my table asserts that the splat book 5e spells are significantly more powerful by level than A5E spells and are as such incompatible.
Anyone with experience in this area?
This. The power level of the spell is going to vary by the design of the spell. Same with all 3rd party content. Some 3rd party companies may have material that fits in seamlessly, some may have over/under-powered content, some may have a mix. That said I've used some 3rd party content in my game (Fateforge, Compendium of Forgotten Secrets, a few others I've found plus some homebrewed stuff) and haven't found the spells to be significantly more powerful.Compatible with mechanics does not necessarily mean compatible with balance.
Well, there are a number of A5E spells that are less powerful than their PHB counterparts, but as far as I know there were targeted reasons for those changes.A spell is a spell is a spell -- they're all compatible. I can't speak to how well balanced the splat book spells you're referring to are, but if they're significantly more powerful than the A5E spells, then they're also significantly more powerful than the PHB spells.
3rd party game designers are often quite worried about making any content that could be seen as more powerful than 05e, as that reduces the chance that GMs will accept it in their games. I have heard directly from more than one designer. Its a real problem, as it can stifle creativity. One company (not EN Publishing) I used to be quite fond of is close to falling off my radar when their Discord made it clear to me that their obsession with mechanical balance was making their content less interesting and fun.This. The power level of the spell is going to vary by the design of the spell. Same with all 3rd party content. Some 3rd party companies may have material that fits in seamlessly, some may have over/under-powered content, some may have a mix. That said I've used some 3rd party content in my game (Fateforge, Compendium of Forgotten Secrets, a few others I've found plus some homebrewed stuff) and haven't found the spells to be significantly more powerful.
I agree with this. Most of the "overpowered" stuff I've found is from individuals (and is closer to homebrewed than official 3PP).3rd party game designers are often quite worried about making any content that could be seen as more powerful than 05e, as that reduces the chance that GMs will accept it in their games. I have heard directly from more than one designer. Its a real problem, as it can stifle creativity. One company (not EN Publishing) I used to be quite fond of is close to falling off my radar when their Discord made it clear to me that their obsession with mechanical balance was making their content less interesting and fun.
Ah, of course. I was specifically thinking about Tasha’s and Xanathar’s.A spell is a spell is a spell -- they're all compatible. I can't speak to how well balanced the splat book spells you're referring to are, but if they're significantly more powerful than the A5E spells, then they're also significantly more powerful than the PHB spells.