My lucky day
Yesterday is definitely not my day. Fail to catch both 2 Giratina (1909/1910 cp) with 15 and 14 balls. But it seems today might be a good day. Used 2 of my 3 CTMs, one on maxed Dragonite with Hurricane, one on maxed perfect Zap with ZC, and both get the optimal moves (Outrage and Thunderbolt). Gonna try my luck again on Giratina!
Answers
I went on a streak of over 30 consecutive excellent curveballs against Mewtwo without a catch; then on my first circle miss (so just a normal curve) I caught it (the third Mewtwo after 2 missed).
Luck is definitely a factor regardless of throw mechanics, unfortunately. It would be nice to earn some sort of guarantee if you can hit some minimum number of great/excellent throws (say 16 and 12 respectively).
I'm fortunate to have not missed anything too impressive. My gf missed a 98 Mewtwo with 15 balls - that was depressing.