Yes but you can't expect every class or even spec to be mandatory. And in reality utility forces one mage into the raid just as one resto shaman has been a staple in most tiers.
WW was popular due to being broken in terms of output in legion, in BFA howeve they don't have a lot of parses on G'huun despite their debuff. DHs are popular regardless of numbers or output and utility, because they are new and "cool". It makes sense for Blizzard to ensure their raid slots to some degree, to avoid having loads of people being forced to reroll from their desired class. Another reason might be that both these classes also have tank specs available to them.DH and WW were already popular in Legion.
The Melee specs that are barely used are SV,Feral and Enhance, might throw in Ret in there as well.
SV Hunters actually have fairly good output as far as I know, imho they aren't represented well because Hunters in general are seen and recruited as a ranged class, by most guilds.
Much like SV Hunters, Feral, Enhance and Ele are lost specs at this point. They aren't popular archetypes, most/"all" good players who enjoy the spec have rerolled or quit and they have a bad reputation. No serious player want to go into an expansion maining one of them, because they have a history of being (perceived as) useless and no guild is actively looking for them.
Even when these specs are doing well in terms of output (like Enhance in Antorus, they even had very useful utility for Argus) only few people want to play them. The only way to change this is by straight up forcing raids into using them, either by making them overpowered for several raids or by giving them mandatory utility. But why would Blizzard do that?
Waiting half an expansion until your class is finished is outright pathetic, especially if the devs outright acknowledge before release that something is not done.
Especially if there is only big raid to come after Battle of Dazar'alor, as most expansions turned out to be three tiered raids and 8.1 is the second tier.
I don't think anyone believes that Blizzard did not release an unfinished expansion.