You've said we don't need starting quality midfielders. I think we do. Yeah, we have other needs as well but I think addressing a CB and a DM/CM first should be our priority.
Raki was never our starting DM, this was and still is Busi's job. And he's not aging good so shouldn't be undisputable starter anymore (but he'll be for 2-3 more years).
You're wrong about FDJ. He has played as a DM for Ajax and was bought as Busi's replacement but he now needs to play as a CM instead to accomodate Busi into the lineup though to be fair we don't really have much other options and Busi-FDJ-Arthur/Vidal midfield is probably still better than FDJ-Arthur-Vidal/Raki or so.
I don't really consider Arthur as a guaranteed longterm starter unless he can improve his fitness.
Soumare is more a box to box midfielder (which we could also use but I think we need a midfielder "destroyer" now even more since it seems we'll have a Messi-Suarez duo walking upfront for a few more years) than a defensive specialist. If we're going that way I would certainly prefer him over someone like Ndombele who seems to have fitness issues and can't run for more than 60 minutes (we already have enough players like this). In a similar price range we can also get a much more proven midfielder in Thomas Partey who has a 50m buy out clause.
But if we're looking for a destroyer with a high upside who can be a key part of our next team once the amigos are finally gone in 2-3 years then Camavinga is our man. Sadly I don't believe we'll get him (because we need money for another 100m forward signing) so let's just hope he won't end in Madrid. RM still have Casemiro at the top of his game at 28 but they are already looking in the future for his replacement. I could easily see a Camavinga-Valverde-Odegaard midfield dominating a Frenkie-XX-YY one we'll have in a few years.
I know stats are not everything (and can also be misleading) because they don't show player's exact role/position in his team, team's playing style etc but if you look at the number of defensive actions (tackles, interceptions, clearances, blocks) then it's clear Camavinga is in another galaxy compared to Soumare but that's understandable because they are different profile of the players. I'm just making this comparision because you've called Soumare a defensive specialist which he's not (I've also included Partey because I've mentioned him above. I don't think there is any chance we'll seriously go after him though).
Sure, Camavinga can flop in a bigger club but I think he can be a generational talent at his position and is well worth a risk. It would probably be better for him to stay at Rennes for another season but we are not in a position to do that (RM on the other hand can and most likely will unless the player will prefer to move to a club like Dortmund - which would probably be the best for his longterm development).
Not from a financial (we can't buy a player for 60m and leave him on loan; we're loaning a 160m player so why not though?) nor from a sporting standpoint (we need improvements in midfield now). Sadly with a club de amigos (and even more so with Setien being "in love" with Busi) behind him Busi's starting position is not in a serious danger regardless of whoever we'll bring.
The same can be said about Pique, Alba and Suarez. I would be really happy if I'd be wrong about at least one of them because this would mean we're making a small step in the right direction but I won't hold my breath.
