I don't think they are that hard to distinguish from each other. Modding: installing unofficial content to the game Config: using vanilla content in a custom configuration

Like I said, I'm also not against custom configurations. But the run posted by OP seems to be using a modded game.

I understand that it's very hard to judge whether or not mods are being used, but I think that the rules should still prohibit mods just to keep things fair and properly competitive. Otherwise you can just gap any time with enough grip and horsepower trough the use of mods. The vanilla content itself does a good job of punishing supernatural performance with engine wear and such. I think it's pretty standard to ban mods from speedrunning. It may be hard to judge, but it can be done with the help of the community to pick out cheaty runs and provide evidence.

Custom configs can still be used. Perhaps make it so that the used configuration file must also be posted together with the video so that it's easier to identify inconsistencies, while further increasing the competitiveness.

I notice in the East coast chase 1 that the two leading speedruns catch up to the AI before it crash into the tree in the end which seems to be impossible in the current build of the game. There for it's impossible to match that time.

I think either everyone needs to run the same version or there needs to be an individual leaderboard for each version of the game. Thoughts?