Lenglet was never brought to be a starter but did a good job in his first 18 months or so. Later he and Pique just got exposed because they are too slow to play together. Add to that "being protected" by an even slower midfield with no legs with Busi, Vidal and Raki and the walking amigos upfront and you get a receipt for a disaster. And then he was probably the one who was the most mentally broken by that 8-2 loss and never fully recovered although he did have some good period last season when Pique was injured and Lenglet was paired with Araujo and FDJ was also dropping back to form a 3-4-3 in the buildup.
No reason to change anything now that things are finally working and he's on his way out of the club but I'm sure if he would get a run of games in current team alongside Araujo he would also look at least like a decent CB in a working team/system like he mostly did in the first season under EV and before that in Sevilla. Tbh If we manage to guarantee a top 4 finish with 2-3 games left (and we won't have chances to win La Liga anymore) I could see Xavi giving Lenglet a few starts to put him in a shopping window, especially if we'll rotate/rest players for the EL.