I admit I'm not very well versed in the Feeneyite question, but it does seem to me that this kind of thing is ad-hoc, circular reasoning.
The obvious stress case that would occur to anyone against the Feeneyite position is "What about a devout catechumen who dies before his baptism?"
The two positions I've seen are:
1. God would prevent that from ever happening or provide baptism of water through some means (this thread)
2. If it did happen, he wasn't elect, so he would've fallen away or been damned anyhow.
Now it seems quite impossible that with 2000 years and billions upon billions of people, there hasn't been *one* single elect catechumen who died before baptism of water.
Those two arguments are just bad arguments, you could use them to justify anything (e.g "one sacrilegious communion means you're a reprobate"), since they're circular and unfalsifiable.
This is much more subjective, I get why Feeneytism exist given the abuses allowed under baptism of desire and invincible ignorance, but in my opinion it makes God out to be one of those classic odious bureaucrats we've all met at some point rather than a proper judge, it makes it seem like Moses, Solomon and even Sancho Panza were better judges who used epikeia.