Ummm.....
This belt moulding keeps out the debris such as leaves and pine needles that will eventually clog the drain slits in the bottom.
Also, your door speaker is exposed to the interior of the door. The water intrusion can destroy your factory and some aftermarket speakers.
Your window regulator is in there and needs lubrication. Water continuously dripping on the regulator will cause rust, even in those regions that rust doesn't exits...... The area inside the door won;t allow the water to evaporate.
Also, your door cards are made of pressed wood and are supposed to have plastic to HELP protect it from the door interior, but it may have been ripped by a PO or a shop prior to you.
Are the belt mouldings NECESSARY? No, not to run a POS on a trail, but you really don;t need doors for that either.
I personally like mine to keep out debris, water, wind noise, and to keep my doors clean and rust-free.
If you can even remotely use a computer, you can find the door window seals (inner and outer) for each door and rear sliding windows. They are completely available and you CAN find them with a search here, but I'm not gonna bag on you about that.