Having a warrior is not a must really. If you are talking about the buff you can still use a scroll in the game currently. There are guilds that went through Mythic EP without warriors.
You do not see every guild asking someone to main another class for them. On the guild in this toon there isn’t a warrior either after he went to graduate school too lol. But they are not telling anyone or forcing someone to change their main. If someone wants to bring in their warrior or lvl one voluntarily on their own then sure they can do what they want.
Even though I play alts I am against making it easier to get stuff essences etc. Cause there are ppl who whine or when a buff happens immediately just hops onto different classes. This spontaneous class hopping ruins the game because of easy alts.
I can understand why Blizzard has to do the catch up system for the new players and returning players to get into the game. But the current players abuse that to have alts stacked up to change whenever convenient even for the smallest nerf/buffs done by blizz