Feats are an optional rule because 5E is designed to be very easy to pick up for new players.
I dont see many people playing wtihout feats tho.
Having feats beeing optional would make balancing the game very hard.

Victor:
The Problem with Vancian casting is first and foremost that it puts one part of the group on a different ressource system than the rest, and this seldom works out well.
As said, you need a very specific kind of campaign and even there it is awkward.

On Rangs:
i dont see how this adresses my point. Yes, there are long range spells in DnD. wether or not you use em at that range will be up to the DMs encounter design.
If you creep around int he Underdark, you probably wont get to use that advantage a lot.
Its highly situational.
The Original Sin games were essentialy games run by a DM that puts emphasis on close quarter combat. The same was true for Baldurs Gate.
I cant think of a single DnD game that made use of the maximum range of anyhting.

Ok. And how is a Hellfire warlock restricted to Vancian casting? Do you have any idea how many video games use that mechanic? How does empowering your class feature spell-like ability by taking damage have anything to do with the system for Spellcasting that is used? I dont see how these two things are related in any way.

1. and the majority of these games dont have spell slots. And what? fallout? those games dont even have magic in them.
The TES games had Mana, im pretty sure youd get mad if they replaced spell slots with mana.
My point still stands, wether or not you have cooldowns is not indicative of beeing a good game or not. Theres good games with cooldowns, theres bad games without cooldowns. Its a systemt hat can be adapted in a variety of ways

2. and even Paizo is realizing they created a Monstrosity and try to backpeddal with 2.0, and people are already hating it.
4E was too much of a change for grognards to adapt to, its still a great system and the fact that 13th age and strike exist just shows that the reason people didnt like 4E was because they had a lot of preconceived notions as to what DnD is supposed to be (and that was 3.5).

3.1: Is this what you people actually believe dont you. Its just flat out wrong.
3.2 no it didnt
3.3 Yes and completley break the game, making playing Dnd at high levles a complete joke, not to mention that its impossible for clases like ranger, monk , fighter or rogue to compete with that.
Wizards can stop time, throw people in pocket dimensions or just make people do whatever they want, meanwhile fighters can attack another time per turn and run fast.
See point 3.1.
Just some results from google
http://librarians-and-leviathans.blogspot.com/2015/04/power-and-utility-for-wizards-and.html
http://zennyonmymind.blogspot.com/2018/10/the-martial-vs-caster-imbalance-and.html

if it doesnt exist, why is it some of the most hotly debated topics in DnD and Pathfinder