I agree with you. Does the lack of height difference affect their twizzles? They've made other errors this season but that's been the most common one. I'm no skater, but I can't really see how height would be a problem for that, especially since their twizzles were so good last season.
The most common lack of height difference related problem is normally with lifts, right? I mean, in pairs also with twists, but lifts are the big one in dance. They haven't been having problems with the lifts - all levels fours this season IIRC. Would the lack of height difference affect step sequences and patterns? I'd think it helps to be somewhat similar in height in terms of matching lines, etc.
They definitely need to figure some things out, but I wouldn't jump to splitting up yet, especially since there won't necessarily be partners available who are the perfect fit.
I know it's a long debate about limitations with sibling skaters - pros and cons. I just think the Parsons are fighting the sibling and the height thing. It seems like they hold back their power and dynamic presence at times. Maybe that has nothing to do with being related or being close in height. And obviously twizzles have nothing to do with any of it. I just see such potential!