They've added a lot of good pieces though, Cech, Sanchez, Ozil, Xhaka, Mustafi for some examples. For some reason they've either never seriously gone after or never been able to land a top tier striker though.
Wenger has consistently tried to hit that home run each summer in regards to needing a striker. Liverpool wouldnt sell us Suarez, Higuain never worked out, and Costa wouldn't be sold to Atletico giving us the chance to sign Griezmann last summer. He went for it again this summer in Mbappe but the difference this year is he realizes that time is running out on his time here and he needed to bring someone in at that next talent level.
With Laca and Kolasinac in, the only weakness I see left is depth at CM and another creative attacker. There's a big drop from Alexis/Ozil to Walcott/Iwobi. Bringing in Mahrez/Lemar would go a long way in filling that gap.
Lemar is my preference. 21 year old with a huge amount of potential and already one of the best crossers in the game. Coupled with the fact that at Caen he played some at CM. He allows us a chance to plug both holes.
I dont see Monaco selling this summer though with Bakayoko, Lemar, and possibly Mendy/Sidibe on the way out this summer. I've heard multiple reports that an agreement is close or has been reached for Mahrez anyway.