No im sure he is capable of doing the maths, but he has made a few mistakes then in that regard, with gomes who could have gone last year to psv and also to bentley and dos santos.
Once again, you win some and you lose some.
For someone in charge (last word) for transfers as long as Levy, whatever strategy they have, there will be at least a few mistakes that can be picked out in hindsight after over a decade in charge. Pointing out the examples with the worst outcome and concluding that a change of strategy is needed seems flawed to me as there will be those examples regardless of strategy as far as I can imagine.
Expecting someone to be in charge for that long without a couple of mistakes to be spotted with the advantage of hindsight seems like unrealistic expectations to me.
It's such a basic calculation though that I don't think the issue is that he is making a mistake here, it's probably something that we are not aware of in Gomes' contract for example that means we won't let him go for free.
For instance, if Gomes doesn't hand in a transfer request, he probably is owed some sort of pay off. Maybe the difference between what we then owe him if we sell him for nothing vs what we may not get from holding out for a fee is negligible, and therefore keeping him around isn't all that thing for Spurs.
There are a lot of details we won't know about. Loans often include deals for the loaning club to pay part (or all) of the wages of the player for the duration of the loan and/or a loan fee. Various clauses in contracts as you mention. The willingness of the player to move clubs and take wage cuts, the agents of course have their say, and so on and so on.
Say player X has two years left on his contract. We could let him move on a free, but we would have to pay half his wages for the rest of those two years for him to accept a move. Instead we loan him out, get a small loan fee and the loaning club to pay close to half his wages. All of a sudden we're almost on a free roll, if he doesn't improve it has cost us nothing compared to letting him go on a free, but if he improves we might be able to sell him the next summer or get him off our books without paying half his wages. Of course he might also perform terribly and the next summer we can't even get someone to take him on a free paying only half of what we used to or get him out on a loan with anyone paying any of his wages, but I think that's generally less likely (massive over-generalization alert). Again it becomes a fairly simple calculation with some assumptions about the likelihood of various outcomes.
If the player then leaves on a free a year or two later it's easy to point out that it was a mistake from the outside with the advantage of hindsight, but it's a bit too easy in my mind.