With submission fees it is free, is it?
There are many stories that can be told that would be harmed by using too high of resolution camera and might actually benefit from something "less". The resolution can change the feel of a film and the camera used should match the story being told. There, of course, are obvious examples in the not so distant past such as "The Blair Witch Project" where they took what was perceived as a limitation and ran with it. There are also movies from earlier eras where a quality of mystery or glamor is preserved because you can't see every tiny detail. In these eras film was used and film at the time hadn't reached the level of fine grain, clarity, or gamma that film stock in more recent times has reached. But it gave those films a certain feel that was appealing for the type of story being told and reproducing the look these days in the digital world involves post-production processing to introduce grain, change the gamma, etc. What were perceived as flaws back then by the cinematographers of the day are now perceived as positive features for those making certain kinds of movies. If you already own a camera, take advantage of what it offers and don't fall into the trap of the resolution arms race (where once 4K becomes the standard, they'll be pushing you to buy 6K, and so on). If you rent, look at the project you will be doing and let it determine the camera instead of lusting after the latest toy.