I think it was made clear that Arteta does have an input, and quite a big one. I can't remember where I read/heard that.
I think you need them to be in sync, there's no point signing a player that doesn't fit the profile. You end up with an Emery/Pepe scenario where because he wasn't his choice he ends up on the bench.
edit: here we go -
https://www.goal.com/en-gb/news/arteta-final-say-transfers-arsenal-little-margin-for-error/hrio5f1u5n2y119t3640234ux
"I know that the situation that we have at the club and the context that we are in, but the club knows my plan," the Spaniard told Sky Sports.
"In January, the situation was that we had to fill some gaps and give some stability to the squad. Now is the moment to make another step forward and improve the squad and the players that we have."
Quizzed on whether he will have the final say on any deals this summer, Arteta added: "Yes, absolutely.
"We have a very strong group [working on signings] and the communication is really clear, not only with [head of football] Raul [Sanllehi], [managing director] Vinai [Venkatesham], [contract negotiator] Huss [Fahmy] and [technical director] Edu, but also with the ownership about where we want to go.
"The margin for error is very, very small.
"The gap between the two top teams and the rest is really, really big and everybody is trying to catch up. The competition is between six, seven, eight, maybe even nine clubs now to fight for those positions, so we have to be very smart and we have to be very decisive when we make our decisions."