erm, considering akuma assist literally beats everything up close, those must be slopping assist calls. it hard to say the other guy got lucky when he gets a happy birthday every game. i mean i get hit by random mashing all the time but usually when i get happy birthday, i know i have messed up somewhere along the line.
this is the only game where you have to respect your opponent at all times.
you should try dual hitting the buttons (press two buttons together). for example, with wolverine, you should do c.l, c.l and assist at the same time. so if the guy blocks the first the hit, if he is good, he will push block the second light and the assist will keep him blocking without giving him a chance to happy birthday or the assist will hit him if he mashes too much. if not it will still make him block and you can mix him up.