Try and use it without thinking of it as a cross up tool. Like, use it on someone jumping in at you.
I used Kanchou assist for quite awhile. It does have its uses, but because of the lack of armor it just gets stuffed by everything. It's more useful in combos and in resets because of the delay, the damage, and the control. In neutral, it just gets stuffed by even the shortest range attacks. Considering Bella's other assists, you really may as well run those instead because they do very similar things and can support you in neutral.
I think you really need to play someone quick and dominate to use Kanchou assist effectively. If you aren't on your opponent all the time, it's going to be stuffed. Usually, the point character calls an assist and then relies on it, but with Kanchou, you call it and then it relies on
you to protect it.
The point about it being difficult to happy birthday: that's really only in a specific case where the opponent is either in hit stun or block stun up until a certain point, after which Kanchou hits and is blocked. Nine times out of ten, the opponent isn't going to be locked down like that from when Kanchou is first called to when it gets to the other side. It's much more difficult to happy birthday a lockdown or a rush punch, because they start throwing out active frames almost immediately. You throw down Axe, you get just that; Axe. You throw down Kanchou, you don't get Kanchou. You get a vulnerable assist that's running directly into the opponent, which can be easily hit by any attack in the game. And then you get Kanchou. The delay is great in resets and combos because it offers unique timing opportunities, but in a real match it's nowhere near useful enough to warrant being used.
Again, the only time, I think, that you're going to be able to safely call and use Kanchou, is if you're constantly locking down the opponent yourself. You need to play a character that can lock down the opponent for a long period of time without assists. You can use Kanchou as a big, punishing reset, but you need to be able to act as your own lockdown assist, because you're not getting any help while Kanchou is out. If anything, you'll probably be in a 2v1 situation, because the opponent and their assist can both be out while you're by yourself trying to help Kanchou cross the road to get to the other side.
I switched to Battle Butt, myself. It's not great, but it works in a lot of situations (even midscreen sometimes) and does similar damage to Kanchou while being infinitely more useful outside of niche situations. You can't do anything to make Kanchou more versatile. The only thing you can do is try to create those niche situations yourself, so that Kanchou can reach its full potential.