So why does it matter then that the game includes them for the 17 people across the globe who actually use them? Or includes equipment weights for the 23 people who use encumbrance? They literally serve a purpose for only a tiny percentage of the gaming populace and could not be any easier to strip out for those who don't want to use them.
Ive come to the conclusion the reason things like this don't mesh well is because they aren't integrated into the gameplay loop. Your encumberance going up or down doesn't induce any meaningful changes in the gameplay other than an arbitrary "you don't have this thing", which obviously isn't very satisfying.
Thats why when I looked at Durability as a system it occured to me to make it so that its both seamlessly a part of the gameplay you're already doing (throwing damage dice) and provides new options to you depending on your roll and your class. Rolling well grants any character Boons that they can use on their next roll, rolling poorly takes away Durability and overall damage.
But then Classes come in and start messing with that give and take. A new Barbarian sub I'm chewing on is going to be all about exploiting the tendency Improvised weapons to break on their first use to chain up into some absurd boosts, and will grow in power even into the epic levels by allowing them to rip off parts of their enemies to use as weapons and armor.
Rip off a Dragons claw and one of its scales, and start bashing it with it. And when they break, now you can either go in for a big attack with a conventional weapon, get an easier refresh by stealing more parts, or you could get other benefits. Im still theorizing what all I could introduce there but the ideas sound.
So long story short, I personally haven't chewed on encumberance much (beyond knowing I favor a volumetric slot system over weight), but the idea is going to be the same there. There will be benefits and drawbacks that will have meaningful interaction with the rest of the gameplay loop, and ideally it'll blend seamlessly into something you'd already be doing.