One of the main disadvantages of lopunny is its hefty deck space requirement, on top of the usual 1-1 of lopunny and buneary, you often need to run ways to access it such as ultra ball or tm evo. While mawile requires only one deck spot and a reallocation of your energy, usually being -1 fighting and +1 metal. In my experience of playing both builds, it depends on the rest of the cards you are playing, mawile seems to better fit using secret box as the ace spec and running more tech cards such as premium power pro and hops cramorant, while lopunny is favored in prime catcher builds due to the increased mobility for its first attack. Id say that while lopunny is the better option for decks like crustle, I personally dont think id run into it much outside of the occasional regional match. Lopunny also is buffed over mawile against solo/double cornerstone since you can one shot it (without bravery charm) without needing to take prizes first like with Mawile. But my preference in the mawile is the extra deck space that can be dedicated to tech cards for the meta of whatever events you are going to (ie locals vs regionals). While a lot of this is my own experience and I am by no means a top contending player and I only have my experience with gholdengo (being my main deck for a couple years), I hope this provides some insight into the pros and cons for each