If LeBron wants to win another ring, he should take a pay cut. But that would only make sense if the Warriors' management improved the bench, i.e., found some good role players. Then the Warriors, with the Curry-LeBron duo, would definitely be contenders for the title.
Lebron can't take a pay cut. His contract is his contract and that can't be changed, this isn't football where a transferred player will have a new contract, you buy out the existing contract when it is in the NBA. So whatever he is making at Lakers, will exactly be the same price what he is making at Warriors if that trade happens.
And in theory, they are capable of making this trade too, it is not really that hard, it's just that Lakers are losing Lebron and getting nothing, so why would they do something like that? Like Lakers could send Lebron and Bronny to Warriors, while getting Jimmy Butler, I think Lakers still have to send some rookie or something to make this work too, in order to cut some costs. But yeah, it works. But why give up Lebron, just to get Butler?