If a mercenary mode would be me, a Highmountain Tauren, getting to queue up with Alliance as a Tauren, then sure. But I don’t want to play my Highmountain in a Night Elf cosplay to be able to group up with the other faction.
Because the conflict is why we can’t group up. The conflict is the explanation as to why people can’t just do dungeons with their friends on the other faction. The idea of tensions between the Horde and Alliance is the reason Blizzard likes to use to explain why we’re still separated.
You keep saying distinct but they can still be distinct even if we’re grouping up together. We experience the same raids and dungeons, so what if there just so happens to be two Humans and three Orcs running it? It also solves the egregious faction balance issue with so few Alliance wanting to do high end content.
Arenas already show AvA and HvH, so why not allow groups to be AH?
Prior to Cataclysm, the story was weaker. Vanilla we were murder hobos and the faction conflict was just PvP server focused (then later bgs). BC has really horrendous lore but the faction conflict still made sense. Wrath was a decent story, but it suffered from the Argent Tournament patch because it indicated how dumb the faction war was, though it still did make a little sense.
Cataclysm was pretty bad across the board story wise with a lot of cross faction helping, but then MoP showed that things could go well. Since then, it has been dreadful.
Many of the decisions made were because of the conflict. To make the Horde even look threatening to the Alliance after a civil war nearly decimated their elite forces, the Alliance had to be written as pants on head children to make absolutely dumb mistakes.
Same with Sylvanas’ retreat horn. Couldn’t have anyone send a letter about the Horde being overrun, we need that faction tension for Legion.
The idiotic decisions are made to maintain the faction conflict, it isn’t a result of them.
Factions can exist but cross play can also exist. If we’re helping NPCs and faction leaders, we can help each other.