The issue is not just the dice and the results, or just the "rng" as if it exists in a vacuum.

The issue is also that the game doesnt provide enough diversity in its consequences to ameliorate for harsh and sudden outbursts of "bad roll". Thats why its a bad roll - that the players save scum - to avoid.
Large majority of instances where a dice roll is performed in BG3 only have an optimal and negative result in how that specific quest evolves from there.
The moments of actual failure that provides other ways to play as very rare and most failure lead only into outright negative consequences.

In that sense it doesnt matter how you calculate the "rng" if the only result is binary.

In smaller side plot situations that is not necessarily bad and can provide some engaging difficulty and necessitate to think outside of the box, but larger more crucial important events of the narrative - that can be played through in the EA - mostly end up as different degrees of straight up failure, either to affect the plot in some specific way or to get important information. The Druid - Tiefling refugees plot stands out as the worst example of this because its badly written and designed from the ground up. It even forces the player to fall on one or the other side of its binary nonsense by forcefully suppressing quite ordinary options players otherwise have. The problem in the trial is not the that dice rolls are high or difficult, its that the options and the results of both failure and success are completely incoherent insultingly simplistic garbage.


The other side of this coin is that "rng" is not supposed to be just random.
The character skills, leveling up, advancements and any gear and items and information the player can find - not only should, but must affect the outcomes. So it cannot just be fing "random". As if the problem is only between two binary options, having complete "randomness" or its opposite, complete determinism.

And that itself is a problem coming from far deeper issues we have as biological organisms that evolved on this planet. That stupid limitation, the tendency to think in opposite, mutually exclusive binary extremes.
Thats the reason why almost all discussions about "rng" devolve into two opposing sides each stupidly holding for their own binary extreme.