This is an interesting point, because maybe a year ago I would've agreed with you. But football moves on very quickly, and players' relative abilities can change quickly.
Just taking a quick glance at the current squad, how strong is our first team? We need a proper keeper without doubt. Baines is getting more and more injuries and his injuries and age suggest it won't be long before we need a proper left back. I would say Coleman has been average at best (being charitable) for a long time now, and we may need to address that fairly soon. Jags is not getting any better and may just be going over the hill slightly judging on recent form. Williams is good, but he's 32 and won't be there forever. Barry is still good most of the time, but will need replacing in the next year or two. A lot of people think we need to sign a better player than Barkley in his position. I don't agree but that's a commonly held view. Both Mirallas and Deulofeu appear to be standing still as players and could be improved on, and there's every chance Lukaku will be away next summer.
You might disagree with some or all of that, I don't know. But the more you look it at, the more it feels like a big overhaul is needed.
I agree with all of that, unfortunately.
Maybe most of those players will improve once they've had a full season and a full pre-season with Koeman and his team.
My instincts tell me that Williams, Barry, Deulofeu (controversial... I just love him though
) Barkley, Gana, and Bolasie will still be nailed-on regulars as next season starts.
Lukaku will probably be off.
And Coleman has been on and off for nigh on three years now.
If possible, I think Koeman would want in the next 2-3 transfer windows:
GK: first choice (Stek isn't good enough)
RB: first choice (Coleman's declining form)
LB: first choice (Baines' declining fitness)
CB: first choice (Jags and Williams advancing ages, Mori being a bit poo, and Holgate and Galloway being very young)
DCM: maybe two (McCarthy isn't good enough, Gana goes to AFCON, and Barry is ageing)
ACM: first choice/serious competition (maybe a different type of player to Ross, a clever link player)
RW/LW: first choice/competition (He doesn't rate Lennon, Mirallas is unreliable, and Deulofeu is mystifying)
ST: Two (Lukaku will leave, Kone is done, and Valencia won't cut it)