Well since summer 2021 the following have all moved and are better options at CF than Jesus: Greizmann, Andre Silva, Vlahovic, Jota, Daka, Malen. That's just high profile players, our scouting network would be looking at promising players for that back up striker role.
But Jesus has been proven not up to it since well before that, i'd say summer 2019, the issue was ignored and has come to a head because Kane didn't join and Aguero left.
We've had 2 seasons of the best manager in the world playing with 1 arm tied behind his back, and now we've got the best young winger in the world playing out of position to cover it too.
We have a world wide scouting network and a unique system of clubs that let us identify and develop talent like nobody else, the idea that we couldn't find 1 up and coming player or promising youngster to replace Jesus (who the manager doesn't believe can play CF) in 3 years is mindboggling.
Good long term planning would have been to replace Jesus prior to summer 2021, that way we wouldn't have been left without a striker when Kane fell through.
Re left back, of course we could have loaned Mendy out and got someone in, he's knees have been permanently bust since late 2018.
Txiki's done a good/great job but left back and CF are gaping holes in the recruitment and have been for years.