Kirk is more proven at the MLB level, not denying that. Even at the time of the trade, I preferred keeping Kirk/Jansen as the catching tandem given the Jays timeline to contend. Moreno had more risk given he was an unknown commodity at the big league level.
The issue with Kirk is if he doesn't stay in somewhat decent shape, it's going to have a negative impact on his overall performance both offensively and behind the plate long term. There is nothing wrong with being concerned about that.
Moreno could end up being like a Jean Segura type bat behind the plate. For Moreno to be valuable offensively, he'll have to hit close to .300 every season, given his low BB rate and lack of power thus far. Given his age, it's reasonable to expect he makes improvements in those areas down the road. Also, he might not. So still more risk if he does regress given the low BB rate and power.
Kirk even if he hits .240 or .250, he'll still be valuable offensively given his high BB rate. Only concern is if he doesn't hit for much power and declines defensively long term. Like I said before, if Kirk can end up like Gregg Zaun behind the plate, more than happy. As well, definitely upside for more offensive output if he takes better care of himself physically.