I wasn't sure if this squad just feels weaker or if it actually is, but a by position analysis doesn't come out looking great.
LH - Definitely weaker than the average tour
Hooker - Probably a slight weakness comparitavely, plenty of quality there but George is out of form and Owens is old.
Tighthead - Could make an argument either way, Furlong's all round game is as good as anyone the Lions have had and I rate his backups too. Probably a position of strength but I'm sure some will disagree. Sinkler missing out on one hand speaks well of the strength here, on the other you could say that him not going means we're not as good as last time. Still, I'd be inclined to take them over the options on most other tours
Lock - Like TH, a position that as a collective we're strong in but negatively impacted by some odd selection. If we have a match day squad made up of Itoje/Henderson/Beirne/Lawes we're as good as anyone but strong chance Gatland shoehorns AWJ in there. Should be a strong point but might not turn out that way in practice. Also Jonny Hill (still don't get it). About as good as other tours.
Backrow - A strong point but pretty much every Lions tour I can remember has had a strong backrow contingent and it's hard to see Simmonds and Conan making it onto many other planes. We also don't have a natural 6. I think we're probably better than SA here and it's a strong group but other tours were probably better.
Scrumhalf/Outhalf - Easily the weakest the Lions have been this side of 2000, in both positions. Not much more to say.
Centre - Bad
Back three - Honestly pretty decent.
In summary, Loosehead, 9, 10 and centre are all obvious downgrades on most tours. Lock and hooker are okay, backrow and back three are both good but not obviously moreso than other tours, tighthead is the only area where I think there's a decent argument we're better than normal.