As Wolfpup said, it’s the details that matter.
Sure, it might be that Trump’s proposal will favour airlines. Or it might not. It depends on the framework of the non-profit corp. In Canada, the directors can’t be union members, airline employees, or government folk. That’s meant to give NAV Can independence from all of those groups.
Sure, Trump may hand over the ATC assets free of charge. Or, he might not. In Canada, NAV Can had to pay the federal gouvernement over $1 billion (Canadian) for the assets. That was in 1996 dollars, and for a much smaller suite of assets. Will the US federal government charge the body an equivalent amount for the FAA assets? Will have to wait for the details of the proposal to come out.
As for the cost-cutting argument, that assumes that the FAA has always been fully funded without any cut-backs for political reasons, and that giving the new agency autonomy would be worse.
In other words, it assumes that the federal budget process already works well and ensures all federal agencies are fully funded as they need. Everyone who thinks that’s a fair description of the federal budget process, please put up your hand!
For example, was the FAA immune from the budget sequestration process from a few years ago? Or did it get an across-the-board cut to its budget, just like every other federal agency, regardless of the effect that might have on safety in the air?
In short, being part of executive branch doesn’t immunise you from arbitrary cost-cutting. The argument is that giving the new body fiscal powers and autonomy will lead to greater stability and more professional allocation of funds, not driven by political “flavour-of-the-month” financial policies.
Of course, whether that will happen depends on the exact structure of the new corporation and the overall regulatory framework. You need to know the details before an assessment can be made.
Finally, in response to the general scepticism that a non-profit can’t do the job as well as a federal executive branch agency, look at Richard Pearse’s comment: other countries have successfully privatised ATC, not just Canada. Is it American exceptionalism that only an executive branch agency can handle ATC in American skies, contrary to the experience of other countries?