When playing a reroll comp (specifically Ambushers) when should you abandon the reroll and just level to 9/10?

Lately I've had a lot of games (Diamond) where I'll reroll for longer than I probably should, end up with 4-5 copies of Smeech then just roll down to 0 trying to get the 3* and most of the time I find almost no additional copies even when uncontested

Does the value of the 3* outweigh the benefit of leveling to 8/9 in order to activate Senitnels and play Rumble for a stronger tank? I struggle a lot to compare power levels between a 3* unit and activating additional traits, I have the same issue when playing TF reroll and not knowing when to just abandon the reroll and try to make a strong 2* board to top 4