Absolutely spot on. Semedo was excellent in the first half, but as you say, that becomes irrelevant when he has effectively cost us two goals in the second half due to poor positioning/lack of effort. We need it for 90 minutes, but he's not that kind of player.
In terms of your second paragraph, I wholeheartedly agree and this is a major concern for me. The lack of fight and leadership in the dressing room and on the pitch is alarming. Neves will say all the right things beforehand & he'll hustle around the middle of the park for 10-15 minutes here or there, but he's not a proper leader. Plus he'll be off in the summer so as you say, he won't feel the consequences of relegation. Behind him, I can't point to anyone who is backing him up. Collins could be that man in a few years but I thought the "young John Stones" comparison that someone mentioned a page or two ago was spot on too. People scoffed when we let Coady go, but we're missing him; maybe not so much on the pitch, but as a character and leader. Then the big characters like Saiss & Ruddy that have been allowed to go too - neither in our best 11, but clearly big personalities. That's all on Shi, Lage & Sellars. Absolute clown show in charge at the top.
Just to touch on an earlier point, as you also correctly state TT, many of this squad will be off in the summer or even during the next transfer window.
Semedo, Neves, Adama, Raul, Jonny, Podence, Guedes, Costa, Moutinho - they all very much feel like they're coming towards the end of their cycle here, or will be sold to make profit if we go down. They also all individually know (bar possibly Costa) that they'll all definitely get nice, comfortable moves somewhere else. Probably on the continent to some nice warm country too. Do we honestly believe they will fight and scrap for the shirt in a relegation dogfight? I don't. You can likely add Nunes to that list too as he won't be sticking around if we go down.
We'd then be left with a list of players like Ronan, Hodge, Yerson, Hwang, Campbell etc. Would that be good enough to come back up? Doubt it.
I think we are in serious, serious trouble; and it's mainly on Shi and co, but the players aren't helping.