He’s good enough to step in and play when needed. Not world class but good enough.
We don't need to sign exclusively amazing top tier talent players. As long as we can maximize the value of our players and use them properly, we need perhaps 6-7 top class players and can fill out the rest of the squad with decent to good players. When you look at City, Liverpool or Arsenal, they've bought many players that were not considered top talent but have been able to be very successful with them - e.g. in defense the likes of Akanji, Ake, Matip have never been considered amazing talents but they've performed very well when called upon and they were able to get them at decent prices (Ake was quite expensive but still cheap compared to some of our signings). Meanwhile we have gone almost exclusively for expensive, highly rated talent and have spent hundreds of millions on the likes of Maguire, Varane, Lindelof, Martinez, Wan-Bissaka, pretty much never going for bargain/value signings and have exactly 0 defenders that would get in any of the top 3 teams.
Leverkusen who have had such a wonderful season under Alonso have basically built their team with freebies/cheap signings and players that were rated as merely decent at best elsewhere.