I think it's fair enough really considering his lack of physicality. We've seen how well Heaven has slotted in, largely I think due to how physical he is already at a young age.
Amass looks a potentially top quality player technically, but he'll need to grow into his body a bit more first before playing mens football.
Either way you never know with these youngsters. Dorgu has come in and looks promising, Shaw is useless at this point and Dalot should never be moved to the left. That leaves room for another LWB certainly, but not someone as high profile and expensive as Kerkez.
If it isn't a youth player stepping up I think we'll want to look for an experienced option at a decent price, ala Maz, to step in and fill out that role.