If you cannot (or refuse to) estimate cost or probability of success in a timebox you have no way to figure out ROI.
To rationally allocate money to something, someone has to do the estimate.
In the real world, if you've got $100k, you could choose to invest all of it into project A, or all into project B, or perhaps start both and kill whichever one isn't looking promising.
You'd need to weigh that against the potential returns you'd get from investing all or part of that money into equities, bonds, or just keeping it in cash.
When devs refuse to estimate, it just pushes the estimating up the org chart. Execs still have to commit resources and do sequencing. They’ll just do it with less information.