This is certainly correct if you think Machado is only a 3 win player going forward and that Moncada's breakout was the result of the position change. I, personally, don't think either is true, but I can't prove it either way so it isn't worth arguing. If Machado now projects as a 4-5 win player going forward instead of a 5-6 win player, and Moncada still takes the strides he takes to become a 4-5 win guy himself as a second basemen, I'd argue the team is in a much better position and still has room to add significant pieces without cracking into top payroll range.
But the real problem I have is this: even IF Machado turns into a bust, there was no way to know that at the time. At the time, it represented one of the biggest opportunities in history to get safe, elite production for an entire competitive window. And the money was NOT spent then. Sure, it didn't go away, but I have to wonder now how much of it was ever really there in the first place. And whatever opportunities exist to spend it now are nearly always going to be lesser opportunities.
Like, Cole now is the prize. But a 31-year old Cole is absolutely a worse buy than a 26-year old Machado was. The upside is similar but the floor is SO much lower. Injury could make him near replacement level at any moment. Every likes to shit on Machado's down year but it was still worth 3.5 wins.
But, all that said: you're right. What I'm proposing is risky. I just think it's the only way this team, given its restraints, can every really get over the top. At least, without a tremendous amount of luck.