Though, again, it’s not just teaching BOD that would make Bellarmine, Liguori, Suarez, Cornelius a Lapide, et al., incompetent if they were wrong; it’s that they understood Trent’s decree on justification to be teaching BOD. If this decree clearly does not teach BOD, as some modern lay people assert, then Bellarmine, Liguori, et al. grossly misunderstood something that should be clearly understood. That means they were either incompetent or malicious
Here's where Bellarmine, Ligouri, etc were wrong, and it's not due to incompetence or maliciousness, but inexperience. Not theological inexperience, nor lack of sanctity, nor lack of IQ...what they were missing is chaos, spiritual warfare, and human degeneracy. They were missing the "real life" application of this BOD concept.
The early Church Fathers lived in times similar to ours. Persecutions, heresies everywhere, antipopes, truth under constant attack. +Bellarmine, +Aquinas, +Alphonsus lived in calmer times, when the Church was not ravaged by spiritual war, when people did NOT question the most basic of truths. Sure, there were heresies of those days, but not to the extent of the early Church nor our times.
So, when +Bellarmine, etc were thinking of BOD, they did not (could not) envision a time when 95% of churchmen believed that Jєωs could be saved, as Jєωs. Or that "all religions are pleasing to God". In other words, their error was in not foreseeing/projecting out the conclusions of BOD, which have led to the heresies of universal salvation/implicit faith. In their day, they were simply thinking of the "poor native indians". They were not thinking of the horrors of V2, the coming one-world church and the false ecuмenism of our day.
These are the same people who "piously believed" that God would not allow the pope to fall into heresy. Well, they were totally wrong. God has allowed it. And God has allowed Trent's "justification by desire" to turn into a replacement for baptism, which applies to anyone who "loves God sincerely". They were naive. They couldn't foresee the future. It's not that they were dumb or malicious. They were just unprepared for the 20th century and V2. How could anyone predict this? A crisis unparalleled in all of Church history.
If they could have foreseen the consequences of opening the BOD "pandora's box" and the heresies to which it would lead, they would've been much, much more cautious, precise and exact in their speculations and theories.