The root of stoicism was the understanding that the only thing one can control is themselves and their own reactions to the outside world. They knew they couldn't control the gods. So, rather than pray to Zeus for bravery or Hera for wisdom, they worked to foster bravery and wisdom within themselves. You can take their ideas and express them in prayer, but if you say that prayer is equivalent to that idea you're just wrong. The prayer adds supplication and dependence upon the divine that stoics rejected.

The god part is irrelevant. The difference in philosophy here is whether you do something yourself or beg someone else to do it for you.

I'm just saying a stoic would work to better themselves rather than asking someone else to make them a better person.

Hang on to that. You might find it to be a useful point of view, in time.

It's literally a prayer, a request for someone else to grant you the desired qualities.

I'm not missing the conceptual parallels. I'm saying that asking someone else to grant you these traits is less stoic than accepting that you lack them now and working to develop them without having someone grant them to you.

You've got it backwards. The serenity prayer is stoicism with extra baggage.

A stoic wouldn't ask a god for these traits; a stoic would understand that a god is one more thing outside of their control and instead work to develop these traits within themselves without the need for a god.