Buffing one player at a time is harder to balance, not easier, and starts to encroach upon Dancer flavor territory besides. We can very very easily look at the behavior of things like Battle Voice, Litany, Chain, Trick, Devotion, etc. to get a baseline for what we can expect from different party-wide buff ideas.

With single target buffs, it's much murkier to calculate what the optimal times look like because you have four dps and perhaps even two tanks to consider for any given window. It's a big wait and see at best, to see what the top AST speedrunners are able to do with the new cards, and even that is a really different dynamic than what's being described.