>>56262477defense form is incapable of being good because of its terrible stat distribution and shit defensive typing. attack form's 180/180/150 is a lot more impressive than defense's 50/160/160. too many points wasted in speed and offensive stats that are still too low to use.
it simply doesn't function as a wall, its only use is to vomit hazards and there are way better pokemon for that role.
basically there's no saving it. same goes for normal form, no matter what you do it's going to be a worse version of attack, defense, or speed. even if you were to average out its stats to 100 across the board, it'd be a worse mew.