Welcome to the forum.
Maybe one of the construction guys has a feel for the statements you are hearing but it doesn't make much sense to me. At a depth of 4 feet you're at around 25000 gallons. The size of the pool shouldn't make any difference to a newbie. Just more water than a smaller pool and more of the same maintenance. Solar covers on round AG pools are generally a PITA to take off and put on so with a bigger pool it's more of a hassle. As for the load on the pool walls....the load is determined bu the depth of the water, not the volume. So, the pressure profile, top to bottom, of a small 4' deep pool is the same as a 33' pool. Now, I assume they use more verticle wall supports on the larger pool and that would compensate for the larger radius of curvature. I also think if there was going to be a stress issue manufacturers would not make the things and warrant them. From a construction standpoint I suppose it would be harder to level the larger area but certainly should not be a show stopper.
Hope this helps and hope others chime in too.
Al