What?
If they add a new MEKA hero, that doesn’t automatically mean they will just be an accessory to D.Va and her lore.
They can get their own backstory, their own lore, their own special personality.
Part of that history can include D.Va, which would be interesting, seeing them compete against eachother in their childhood or something. Seeing it reflect as a strong bond in their new careers as adults.
But limiting D.Va as the only one to have a MEKA because you’re afraid adding another MEKA hero will take away that unique quality that she has one?
That’s silly.
Did you know Wrecking Ball also has a mech?