I’ve not had issue on any classes (excepting mage and priest that I just level to have my 12 classes at max) in Legion Mythic raids, with only non-group content gear in Shadowlands, but then I don’t often do ToS because it often doesn’t have my preferred transmogs.
And it seems like almost all the comments about ‘Legion Raids’ not being soloable all are specifically ToS not being soloable (Avatar, KJ, etc…)
Which makes sense, ToS has a number of ‘insta kill’ type mechanics if bosses take longer to die.