It is the responsibility of the vehicle manufacturer to select tires appropriate for the application and to ensure that the load capability of the tire is sufficient to meet the stated GAWR.
Now sometimes an RV company may even lower the states GAWR to avoid having to select larger (more expensive) tires. This has been seen when 6,000# axles were de-rated to 5,500# so the two tires only needed to be capable of 2750#. Obviously this does not address the fact that RV companies are aware of that many users often exceed the published GAWR.
Your calculations of load shift and side wind forces are also something a competent engineer working on vehicle design would / should IMO take into consideration.
I agree that it would be good if there were some stated margin such as 15% load capacity. While this would not eliminate tire overloading it would significantly lower the probability and number of overloaded tires but again lobby efforts from the RV industry would IMO work against the adoption of such requirements.
I write a blog on RV tire application and safety. RVTireSafety.com
Also give seminars on tires at RV events across the US. 40 years experience as tire design & quality engineer for major tire mfg. Freelander 23QB on Chevy chassis is my RV