I don't particularly love my baby not having the upper hand/being choked either, but with both those instances I took it as her being distracted and taken off guard rather than being weak. When she confronted Zelena she was distracted by her worries and self doubt because she wasn't convinced yet she had light magic in her. She also had Robin and the others being attacked by Rumple and monkeys so there was a lot happening. It made sense than Zelena sensed that fear and struck, but ultimately Regina got control of her emotions and when she did we saw she was more powerful and easily took care of Zelena.
With the Snow Queen, she was distracted by Sydney’s betrayal and Emma’s presence, plus the whole Marian situation. She wasn’t going to attack the Snow Queen right away since she wanted to get her to unfreeze Marian but her moment’s hesitation was a mistake and that’s why she was put in a choke hold. This is just how I interpreted both of those scenes.
I don’t think either made Regina seem weak, merely human. I think when she’s focused her magic is always shown as being among the strongest.
