King Rad
Warlord
It's a 2.5 percentage point increase. Twice the proportion of players of Civ 6 have completed Deity as compared with Civ 5. Sure there's selection bias, but seeing as this is the only stat that can be compared directly between the two sets, I'd say it was significant. Not conclusive, certainly.
Unfortunately, even that is not a real comparison since V would not have included deity wins where the player was using mods. I usually play mid-level [prince or king] and have no interest in getting lowest turn win, etc. I just play for fun and I play through each civ once before going to next civ; but I use mods [nearly always the unlimited experience mod from barbarians, since I generally play peacefully plus i think it's fair to gain experience against later bards since their tech increases as the game goes along] so many of my finishes in V would not have been counted, while they are in VI [I usually finish my games - and now I'm trying to get the final DLC civs completed in time to start the new civs for Rise and Fall!]. Bottom line, not counting mod games for deity level in V is probably enough to account for the difference in percentage of finished games.