If you mash it out, chances are you'll be too high to land and do the 5C. I usually delay the last hit a bit. You have to really be in the corner as well, if you have to dash forward even a little the 5C won't connect.
I feel the timing if the 22C links is more or less the same as CSE, which means 22c 5C is always annoyingly hard to place. What the combo thread seems to hint at, however, is that the 22C routes aren't even worth the trouble anymore damage-wise.
I feel it depends when you hit with Mami? I think it's only a matter of when you recover, if the enemy was in the air, etc. When it hits right, you can do the 22C from where you landed and it'll connect.
Most of the time I see the 2a pop-up and combo is when the opponent is down and you catch them rolling or not teching with it. It has an "S" combo rating, so there's not much you can do imo. I usually see 2A>5A>6A> stuff from it.
Worth it when it kills : D
Pretty much every item aside the cat hammer can be used as combo tools now and extend combos that would just do less damage if you didn't user the item. Using items for neutral AND combo tools is the whole point of the character if you ask me!
Also, 5C knockback is one of the reasons Moy quit the character so... yeah, it's intense :3