I agree that main gun crit has no sense, is not a calculated risk like abandoned tanks that you can lose in enemy territory, is simply 1v1, one shot and enemy is dead cause i started a good engagement but no, main gun crit and bye my tank. It's completely out from any kind of strategic logic.
This is really not true. Crits only appear (except from a units activated ability) after the tank's health have dropped below a threshold. Also destroyed gun is pretty benign since you can just back up. This is the RNG "tells a story" that Relic wanted to introduce, abandon vehicles is the kind that makes tournament play look silly when someone wins because a PIV gets abandoned by a single zook (or something stupid like that).
If you dive deeply and cannot pull your tank back you run the risk of not being able to finish another tank. This allows injured tanks which need to back up a chance to escape from combat by making offensive actions more risky.
Not all RNG crits are bad, not all are good.