slider photos resolution

Hello, as in title, I’m having bit of trouble with my slider photos resolution, I am aware that the theme recommendation is 850x500px but my photos are natively 4013×2166 or more and the downscale to that is devastating to the photos, I’ve been trying to find a sweet spot and stopped at 1170×500 but them photos look really squished. Any tips or suggestions ?

Edit : fj-tools.nazwa.pl/wordpress

Edit 2 : I was messing with the theme css as well and i messed up the footer trying to take down the wordpress usage bit, could you post the code for that as well ?