If a professional sportsman isn't at their optimum condition by the age of late 20s then I'd suggest there isn't much hope. Ifs and buts don't get you far - we need to deal with what we have.
I think Lui has been carrying a couple of knocks this year so maybe a few months off will do him good. He is certainly not a bad player - I just don't think he is in the same category as Danny Mags was.
Our main priority is a prop, we all know that. But after that? We are stacked for back rowers. Gale has 7 locked down. Centres are fine as long as Newman recovers. Wingers are also fine by me for the moment, and we have young Tindall coming through. Full back Myler or Walker? Walker is still very young and should improve... so for me the next weakest link looks like 6.
I suspect we will recruit a prop and pretty much leave it at that for 2021 (and McLelland needs to push his spot too). We will see if Lui goes well next year but we lacked zip on his side for the final few fixtures this season I felt.