Jester David
Hero
Just FYI, now you're confusing an AL rule for something affecting our home games.
There's nothing saying you can't play a PHB class with Volo race with a SCAG subclass and a EEPC spell...
AL play is only assumed in the AL forum ☺
They've recommended it for other games and said that one of their design assumptions is that you're only using one book. Either because of AL or because you're not a collector that buys everything. They're not doing the 4e thing and assuming you have everything and that everything is "Core".
It's more like 1st Edition where options aren't being assumed beyond the core rules in future books and supplements, hence why monsters were reprinted in Tales from the Yawning Portal. (Only more so, since 1e did assume you'd have certain monster books like the Fiend Folio...)