And on a personal basis, I'm curious as to why I have suspicions towards the system in this game, whereas I didn't bat an eye in any other : from Tactics Ogre and Baldurs Gate, to Darkest Dungeon and dozens upon dozens of other titles.
Did you play any of these games Ironman? Most of these are more forgiving by design, i.e. there are easy ways to recoup your loss, no irreversible consequences for fail state, simply no stakes.
It is not really about the dice. Players complaining about are not sure what they really MEAN and WANT. Developers who argue against or placate don't get the point at all.
It is about the stakes. A gambler who won 49 coinflips with a $1 stake but then lose a single coinflip with a $100 stake will complain about bad luck and injustice simply because it is a net loss.
BB has a lot of high variety sequences that cascade out of player's control from the same input, to both benefits and detriments. To-hit. Morale check. Damage roll. Injuries. Head/Body hits. Etc.
Character building compounds this further. The whole stars and stat rolls aside, a lot of perks exaggerate the above problems. Sure there are also ways to improve the odds but ultimately it is still dice dependant.
Losing valuable troops in BB is very punishing to both progress and player mentality. It takes hours to find keepers and level them up. Players are also understandably invested in the process.
It matters not how many triumphs one got through, they die then they are gone.
tl;dr: By design, BB is simply a very dicey game with very punishing fail states. What dice is used matters not.