Difference is we get downright world class quality with Koulibaly and 30m for two fullbacks will get us most likely two Roberto/Dest clones. Unless we have a scouting masterclass - something I wouldn't bet on (and quite unreasonable to ask for).
Would be nice to have a strong center for once.
It surely would. But we are very thin on FB's, it's not only that it is Alba and Dest, the problem is that there isn't anyone else lol. I don't want to keep moving Araujo to RB even if he does fine there. At LB I can't even remember the last time Alba was rested.
Obviously getting Koulibaly and maybe one fullback would be the most ideal, but it would cost a bit unless we can negotiate Kouli down even further.