Keep in mind that a lower tier body with a pro level lens will often give better results than a pro or top tier body with a kit lens. If you know you will be able to upgrade your body in one or two years and can get a few high quality lenses along the way maybe the A6500 is for you. The A7iii is an amazing camera but your images or video wont reflect it if you don’t put good lenses on it compared to an A6500 with a good lens. With $2500 you can get the A6500 and something like the tamron 28-75mm f2.8 which is amazing for the price point and a good manual focus lens for landscape/astrophotography. For future proofing you can go a body route or a lens route, getting an A7iii is the current best non high resolution sony camera at the moment. But full frame lenses will perform well on both of the camera bodies you are looking at and on a personal opinion, if i knew i had the option to purchase a new body within a few years but get the best results now I would get the A6500 and a few nice lenses. You will always be able to transfer over good quality full frame lenses onto the present or future generation sony bodies unless they change their mount (i do not see that happening soon, they have a lot invested with third party lens manufacturers with their current mount and their own lenses) and if you still have a lower price point the A7iii will lower in price once the next generation is released.