For me, the problem the Lions face is the same one they've faced for the last few tours, the half backs. Probably in pole position at the moment are the English half-backs, and they are okay but not what I'd think of as Lions test half-backs (maybe Youngs when he is at his best, but he is inconsistent). Sexton keeps looking like he should be and then doesn't quite perform to expectations. There are any number of good forwards, centres, FBs, wingers, but all the candidates at 9 and 10 have their limitations.
The likes of Gregor Townsend, Rob Andrew, Dewi Morris, Matt Dawson, Mike Phillips, even Stephen Jones were not really up the mark, on recent tours. Honourable exception - Robert Jones (and Howlers would have been).
F/B is ridiculous, you could take any of 6 excellent players (Hogg, Kearney, 1/2p, Byrne, Foden, Goode).