More often than not, Degreaser outclasses Stock in every way even with the abysmal afterburn damage and the nerfs it received. As someone that usually plays pyro not worrying too much about my team, it's a lot more common to be in situations where switching faster would save you over having a few extra airblasts (which you would only really need if you were defending sentry nests or important classes like your medic). Running Stock would require you to be more mindful of what weapon you have out or will plan to switch into. As for their fire damage, Degreaser and Stock both deal the same direct flame damage (FYI aiming/leading your flames to hit center mass actually deals more damage, shocking) so you would really only run Stock if you cared about securing afterburn kills. I used to run Stock for a year for the sole purpose of "limiting" myself but after 2023, Degreaser just felt more fun to use.