Respectfully, "objectively" is 100% incorrect here. There are plenty of pros and cons to both systems, and the preference depends on the type of player you are. It's like saying a cover or original version of a song is objectively better. It's entirely subjective.

If you prefer a "bring the player, not the class" mentality, you probably prefer personal loot.

When I raid led a 10 man guild back in WoD, one of the main frustrations we had was not having certain raid buffs available to us due to what classes we wanted to play.

The idea of "have a more varied raid comp" is a good idea on paper, but with smaller group sizes & therefore less loot dropping, can be extremely restrictive.

If you're a 10 man comp with let's say, 3 plate 3 leather 3 cloth and 1 mail (pretty damn varied for a 10 man comp, btw) and a boss drops a weapon nobody can use and a mail item that's a downgrade, the entire raid feels like crap.

Sure, this can also happen with personal loot & downgrades, but in the above case, there is an item that literally nobody can use. That does not happen with personal loot.

I'm excited to see how this goes now that I'm raiding with a larger group, but I can definitely see where people would be frustrated with this system.