WoD will always be the worst. Because not only the features they added during the expansion were bad, but it's also the expansion where we lost the biggest amount of features :
-Garrison was a good idea, but it didn't increased the quality of openworld content (because there wasn't any open world content at all). It actually made it useless because you just had to stack alts to get stuff.
-Shipyard was a worse version of garrisons where your followers could simply die in a 91% mission.
-Only 1 true major patch.
-They removed gems, half of the gear enchant, profession perks.
-They also started the ability pruning.
-Also was the expansion with the most cutted content.
WoD still had good content. Its dungeons and raids were goods. You know, the things Ion Hazzikostas used to work on
.
BFA is not the best expansion and has its flaws. But I actually think it's one of the most daring expansions they've ever made. They've tried a lot of things here (azerite traits, essences, a new way to design items with use / proc, visions, island, warfront) and while I agree that most of those features were not well designed (because of the grind, the way to get essences, warfront is just boring and island don't have any good directive line) they still tried to bring something new to the game.
If you want to blame BFA's class design, blame WoD and Legion. Because BFA didn't brought anything major in class design outside of azerites who are, if you're not a min / maxer, a good feature that gives you the opportunity to adapt your build and who can in a few case change the way you play your class by adding a Divine Storm in your melee rotation thank to a proc for example.