gen1 seems stable for some time, but gen2 are still evolving wich renders in remarkable delays in integration support. Year and half ago, new fw broke integration and it took more than month to update integration (some devices had issues even half year later). not that it cannot happen with mqtt but you can update settings immediately not waiting for devs. (and tbh gen1 mqtt didn’t changed for 3 years afaik in a way it required changes in settings)
I’m aware mqtt integration might change (recently have changed), a bug might be introduced to mqtt addon (which I use) but at first those are not so many updates, at second user base of mqtt is way wider than shelly alone, so probably those components get more attention from devs. Anyway number of issues I experienced with mqtt differs by orders of magnitude comparing to issues reported by users of the Integration.
anyway with the integration you still cannot:
- change light attributes (brightness, color) having shelly entity turned off (without turning it on)
- configure switch as light
- replace one device with another without changing name/id especially when changing its type
- change shelly device ip address
- there are problems with removal of shelly devices from the system (see How to delete a device / entity in ha - #10 by petro)
Probably lot more issues related to limited flexibility.
I’m not here to convince any one (or maybe I am 
) or criticise devs work. Just giving idea how advantageous is using mqtt integration comparing to native one. Especially if the only argument against is presumed higher complexity.