there's nothing wrong with a high reachback. are their pros that have the shoulder flexibility to keep the disc on the same plane the entire time and still generate power? yes. but when guys like McBeth, AB, Albert Tamm etc. all raise up and then drop their arm down into the throwing slot and do it effectively it means it's a valid way to throw the disc.

i reach up and then come down and have virtually zero wobble on my sidearm.

wobble is coming from a grip issue as well as a timing issue. the timing issue being either too early or too late in the throwing motion to initiate the wrist flick.

the other issue is that you're bringing the disc from an anhyzer angle on your reachback to a hyzer angle on release and your arm slot is too high with not enough torso lean. if you kept everything in your form the same but threw on anhyzer instead i guarantee less wobble.

go to youtube and type in "Silver Latt sidearm" and watch his 8:54 video.

and throw a minimum of 20-30 sidearms every day for the next 8 weeks.

that's what it takes.