I am saying that right now, the weight system is a terrible mechanic in most games, designed merely as a patchwork solution to fix up other shortcomings (such as terrible economy).
You conclude that the system is "terrible" and "shit" but don't explain why. The weight system is there to limit the amount of stuff you can carry and if it is successful in doing it means its working, regardless of how it manages to improve or not the other departments of the game.
One should ask himself why such a mechanic even exists in the game's scope
Its there to:
1 - limit the amount of gear you can bring with, you forcing you to commit to it, and learn to make the best use of it.
2 - force you to make choices of what items are you going to loot and punish greedy behaviour - i watched players get killed on the way out of a dungeon because they couldn't run for being over encumbered thats C&C and my idea of fun.
and the answer is usually that it'd destroy the in-game economy if he could just pawn it all off in a shop.
Well its not really the whole reason as you might have seen from my examples, the weight system has other purposes. Games economies are rather fragile and break over a matter of time.
But why would being able to carry everything speed up that process? Because the game wasn't design around the adventures of Jim the Vacuum Cleaner. The devs clearly didn't want to make the default way of playing their game the way of the hoarder.
There is a way to fix this. Very little amount of loot to be found in dungeons, which i am in favor of, but would not answer the tactical aspect of gear choice since i would be able to bring with me a bow, for fighting enemies at range, a hammer, for smiting undead, 2 magical swords, one with ice damage and the other of fire, etc.
So, to preserve in-game economy, we now have the player either going back and forth between town and dungeon to sell his shit (as he is greedy and wants the money) or stopping every couple feet to swap cheaper item in his backpack for a more expensive he just found.
But no decent RPG forces a player to go back and forth for this. Thats the player's fault. Why is he doing that? It sounds so boring! The game was not designed around it, so why do it?
Why not pick, from the loot you found, a number of items and move on? Because you can't? Well thats a flaw that you have and you shouldn't ask the world to change around your flaws and preferences.
For example, Underrail didn't had a weight system. Then it got one but few enough players complained about going back and forth so they could sell more. Styg fixed it quickly with how merchants only buy a certain amount of items. Problem solved.
Not really, these people couldn't stop scratching their skin thinking of the unsold loot. There was even this guy that was catching hoppers and selling them for money. That was so much trouble for so little gain. He would make 10 times more if he went on a mission and retrieved the firearms from the defeated enemies.
The game doesn't force you to do anything like this . You did. The game is built around normal people but it won't stop anyone from going back for more, but its his choice.
My argument is that rather than force this tedium upon the player, a better approach would be to simply fix the damn economy so that it doesn't need such shitty workarounds to stay alive. Maybe not make everything sellable in the shop, or just don't cover every square inch of the dungeon with shitty loot.
Play a game without forcing yourself to do it. Play underrail and leave some items on a shelf. Consider this therapy.
Its okay to let go.
You seem to imply that the weight limit provides some depth. It doesn't.
Yes it does. It isn't the deepest mechanic in a game, sure, but a game doesn't become deeper without it, but the opposite. Now a game without inventory restrictions might be shallower because of it.
This was the case of Underrail before it had some.
It doesn't provide any real challenge either
It might. On Ultima Underworld i had to dump plate armour for chain mail. I lost damage resistance so my character was now more vulnerable making the game more challenging in the combat department but now i could bring other items with me that would make going through other parts of the game more easily. You are asking for a game where i don't have to make this trade. Where i can have it all. Bring it all, have it all.
If you can make the weight limit into a meaningful mechanic that has a different purpose than just trying to cover other shortcomings of the game, then sure, I'll be all for it, but not when all it does is be a source of annoyance.
The weight limit is just one of many ways of restricting your inventory and it is in my opinion one of the most elegant solutions. If you have an inventory with 4 slots, and you can either fill them with either 4 diamonds or 4 chairs it ends up feeling kinda stupid. If items are limited by weight it makes more sense than i can carry 100 diamonds but only one extra piece of armour with me.
A good inventory system should be restricted in multiple ways. Again, Ultima Underworld did this well by limiting the inventory both in space and weight. You could have a box with several pouches inside of them and each pouch had a limited amount of items it could carry.
From what i read from your post, your complaint is not of wanting something deeper, but that you dislike being forced of leaving loot behind. You aren't only against a weight system you are against any inventory restrictions that limit the amount of gear/loot you can lunge around.