What's your evidence that they are getting free $40/plate dinners?
I remember when Huntsman senior made a private plane available for Pres. Hinckley back in 1996. Here's a news article:
http://www.deseretnews.com/article/496659/HUNTSMAN-OFFERS-USE-OF-JETS-TO-LDS-CHURCH-LEADERS.html. It wasn't even for exclusive use by LDS leaders, "The Huntsman family and business are happy to provide the aircraft for a multitude of humanitarian, charitable and business purposes...No single organization or group dominates usage." I haven't heard anything about one or more private planes since then. My brother-in-law's father was a GA (died maybe 10 years ago; to my knowledge he never flew in a private plane. The sister of one of my friends is a current general authorities (young women's presidency) and as far as I know she never flies in a private plane. I suspect the Huntsman plane or similar one is still available for Pres. Monson should he be in a condition to travel, but I think your claim that GAs routinely use private planes is hogwash. If you have evidence to the contrary I'm willing to listen.
Now this one wouldn't surprise me. I know lots of people who use company cars, that aren't even especially high up in their company.
Where's this coming from? The GAs almost certainly have the same health insurance that I do, namely DMBA. (As a BYU professor I'm technically employed by the church.) It's fine, but frankly not even as good as the health insurance I had at my last job, in Wisconsin.
Where's this coming from? I've never heard anything about free education for families of GAs, and doubt you have any evidence for this. At best perhaps they get 50% reduced tuition at church schools similar to university employees here at BYU.
They do likely get retirement benefits similar to what I get as a church employee, namely a retirement plan and access to a 401k plan.
As to whether the actual remuneration and things they ACTUALLY receive put them in the "lavish" category that's still open to interpretation. I still don't consider $120K/year to be "lavish". Consider that these are all mid-to-late career individuals who are nearly always top individuals in their field. Consider my field, namely physics. This government website says the mean annual wage is $122K.
https://www.bls.gov/oes/current/oes192012.htm. So mid-to-late career individuals who are at or near the top of the physics field are probably more like $190K (the 90th percentile number). Or consider your field... you're a dentist, right? The same website,
https://www.bls.gov/oes/current/oes291021.htm, says that the mean annual wage is $154K, and the 90th percentile number is "greater than $208K". And we know that many of the GAs come from law, medical, and business backgrounds, which undoubtedly have much higher numbers than those.
So let me ask you... if you think $120K is too large, what would be appropriate compensation in your mind for someone in physics, dentistry, law, medicine, business, etc.--probably among the top in their field, in his or her mid-to-late career--who then becomes a full-time GA?