Hey Paul...
No lefty would be fine as the elbow moves horizontal..
It’s only lifting the elbow up higher / further back or fully holding the arm out straight and slightly raised like ‘high sticking/euro’ that irritates the shoulder.
I can fish all day on rivers casting to usual fishing distances absolutely fine, no issues until I start casting past 70’ and even then only with the repeated casting you do when practicing...
So it really isn’t a problem for my usual fishing in any sense, just sustained practicing distance and fishing ‘euro’..
I think I could probably still relax my right arm and grip a bit when practicing casting further... which would help, but it’s a hard habit to break
The West Country rivers I fish most regularly mean I change my casting style all the time, I usually fish neutral/closed if casting over head (especially if targeting rising fish or any time needing to be really accurate), but I probably spend at least 50% casting off the side or under the tip due to overhead tree cover.... and then all the usual random ways of casting in tight situations.
I was pretty chuffed yesterday... 5 x 15cm targets, in a sort of W shape at differing distance 7-15m... laid them out and cast to them pretty much as soon as I hit the field...
three turns at casting at them... so 15 casts
Landed the fluff on 7 of the targets and was within 8” of all but 2 of the rest... the best I’ve done when first hitting the field....
Closed stance
.... alas one of the poor casts was damn near a feckin metre off
I must have switched off!
That sort of distance I can cast and practice as long as I want without any issue....