Where did I say they were the same thing? I said they were part of the game, and they are a part of the game in every game I've ever played that has inventory and/or spells. Some games limit inventory, for example, by weight, some by the number of slots.

So clicking a new element to open a new interface every time I want to use something is less tedious than opening the existing interface, and assigning the spell/skill/item to a hot bar? Damn, games have been doing this "wrong" for decades then, yes? If it's going to be "but I can do it once, and add it to a quick slot", then they could spend their development time on more important things, like adding a mechanic that informs the player that one or more of the comps have story beats to advance, and they need to do it in camp, because we can already just add whatever to a quick slot. If you're convinced that clicking multiple elements, every time we want to use an item/potion or spell, is less tedious, then we have very different definitions for tedious. I much prefer locking the hot bars from having items added or removed, and putting whatever items/spells on a specific quick slot once, and referring to that quick slot when I want to use it. Once and done, unless I swap a spell out for a different one, then I have to change it once, and can do it while I'm doing whatever I needed to do to swap it out. Add/use a hotkey to swap bars, and it's already more convenient/less tedious than opening the spell book/scroll case/potion case etc. and using whatever. Which seems rather user friendly to me. That may be why it's been a thing for as long as it has, yes?

Concerning optimized, my set up is pretty optimized for what I'm doing with it. Contrary to the argument made which led to me providing the spell chart previously, there are plenty of quick slots to take us to max level, with loads of empty quick slots, just adding spells. Hot bar optimization is up to the player. Not because devs can't make an optimized version, but because players are going to want very different things from the hot bar. I want very different things on there between different classes. My rogue, for example, has ranged skills on the top part of the bar, and melee skills on the bottom row, but my sorc has spells/cantrips in those slots instead. Different versions of optimization, with the only thing that changes being the class I'm playing, and how I'm playing it. That rogue, for example, my have all their arrows/bolts assigned to page 2, so that I can swap to that page, and select which arrows I want to use. I can arrange them however I choose on that page, which means that I have full control of how optimized that page is for that rogue. I may well want something different for a different class. If we had bards, and they had different songs, I could set them up there instead, or I could put them at the end of the second row on page 1. This makes them convenient, fully optimized for that class, and user friendly, since I'll know where they are, and how to get to them with a minimum amount of effort, including setting them up to my tastes.