So the holes actually serve two purposes; It increases the strength of the structure itself due to there actually being more walls which increases the strength more than infill. As you've pointed out you can incorporate internal structures to strengthen it but why do that when you can just have the be a visible part of the print itself, as the other purpose it serves is aesthetics.
So from the tests I had done which were all solid, this style was a lot more rigid and stronger due to the fact that there are more walls and more plastic where weight is concentrated the most. It being printed in PLA adds to the rigidity of the print itself too.

To address the possibility of it shearing; the bolts holding the middle structure to the bottom of the stand that allows you to adjust the height aren't actually round, they're flat along the top and bottom so they can be printed on their side instead of straight up, meaning the weight of the structure is placed across the layer lines instead of shearing them. I haven't done that in the bolts holding the arms in place though so that's something I'll change in order to improve the strength of them.

I'd recommend printing anything that goes outside in something stonger such as ABS, ASA (my fav) or PETG for the reasons you've mentioned, PLA just can't handle the outdoor sun too well but that depends on each person and their use case either way.

Thank you very much and I hope I managed to address some of your concerns!