The gemara says R' Meir asked for mercy on him that he should die. The tzla"ch says he was a rosho gomur, and so it was better for him to die, so that his z'chusim wouldn't be paid in this world.
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The Maharsho addresses how one can pray for another to do teshuva, if Yiras Shomayim is only Biydei Adam. He explains that the Tefilla was for the biryoni's nisyonos to be taken away, so that he would be able to triumph over them.

Farshideneh Greenstein says: On this it is written "If not for this verse, the legs of 'sonei yisroel' would be weakened."

We quoted this Maharsha in shiur this morning, and we were left with the question, if one can daven that Hashem intervene on the behalf of someone else, and it'll work, where is the bechira for that other person?

Hashem could change the circumstances of that person's life, without forcing them to make a choice. For example, if a tzadik prays for a rasha to turn awaw from his evil, hashem could provide more chances for the rasha to preform mitzvot and fewer chances for him to preform aveirot - which doesn't affect the rasha's free will - he can still decide to be a good or bad person, but it is easier for him to be a better one.

I think critic is right, but yadfo, you have a point, that seems to be what the Maharsha is saying.
But it's still a problem, because if the nisyonos are easier, then he's not really a tzaddik, he's just masquerading as one. And if such a person is called a tzaddik, then every rosho (or at least most reshoim) have a "ta'anah" on the ribono shel olam.
The Gemara (somewhere) says, (paraphrase) "If not for this posuk (a posuk that says Hashem created the yetzer horah) the legs of 'sonei yisroel' (a euphemism for Klal Yisroel) would be weakened." Since G-d created the evil inclination, we cannot be held fully responsible for what we do. Presumably, tracing the yetzer horah back to G-d does not remove our culpability. We have bechira.
But in this Gemara it becomes apparent that there is some variability in the yetzer horah, and if so, we may have a legitimate claim, that given slightly easier circumstances, we may have performed better.
That's what I meant originally with "Farshideneh Greenstein says" but I was typing with a baby on my lap.