Like some other folks, I went from the Nikon D750 to Sony A7III (and now A7IV). I enjoy the mirrorless experience much more than I did the DSLR - autofocusing being a huge advance. I'll add to what others have offered about lenses. I think the Sony ecosystem is also an advantage there. The third-party lenses, many of which are less expensive and still quite good, are still first-rate since Sony has an open standard. I have a number of primes from Samyang/Rokinon and zooms from Tamron/Sigma that I really enjoy and perform as well as my Sony lenses (my camera caps at 10fps anyway). I also had some third-party lenses on my Nikon and always felt they underperformed and could stop working with the next update (though if you are interested in older lenses, there are certainly more around for Nikon F). Don't underestimate the value of the camera ecosystem.