Two comments to this.
One:
I felt they fixed the magic system in 4e and dramatically prefer the A/E/D power system over the old 3e spell system. Why? Because I didn't like the fighter<->wizard power divide, I grew tired of looking up spells in game and losing time, and I didn't like having to hope I picked the right spells for the day or poring through multiple books to find the right spell for the next day.
I'm not mentioning this to have a debate over which magic system is better because the answer is incredibly simple - the one you personally enjoy the most. But I'll come back to this in a moment.
I am mentioning this because clearly 5e has reverted to most of the things I disliked in pre-4e magic systems. Yes, I realize it's not completely the same, but it is the return of spell lists and the power divide and looking up spells. I consider this a huge step backward but that's because I don't like the "old" magic system. However I don't feel "screwed by WotC" because of this. WotC is a business, and as such they exist to make money. If what they feel they must do to best make money does not sync with my preferences in gaming, then so be it. It's not personal, it's just business.
So yeah, releasing 5e is kind of like them telling me they didn't care that I liked 4e, except for the fact that WotC did not make their decisions with my specific tastes in mind. No company is going to cater my specific tastes and it does me no good to take their decisions personally...because they will never be personal.
This time WotC sifted data and learned that the caster-martial disparity was not as big an issue amongst the overall player base as previously thought. It was another example of a few loud voices causing them to make changes they didn't need to make. They lost caster players that were happy with the previous system because they didn't bother to check what kind of magic system caster players wanted. They just focused eliminating the caster-martial disparity due to the loud voices and ended up alienating a huge part of their customer base with a magic system that did not satisfy them. That is a completely different approach to 5E where they tried to make martials happy and actually took the time to find out what caster players wanted.
No. They did not release 5E and tell you they didn't care. In 5E they accepted that you were an outlier on their data, apologized that the game didn't please you, and released the game that would attract the largest portion of their player base, including the caster players they lost.
That was very different from 4E where they didn't do much play testing. Didn't do much data sifting. They released a game we hadn't seen much of like did 5E and told us, "Here it is."
Mearls was much more careful. He sifted data for a long time and continues to do so. He ensured that the game they produced was going to hit wide. Even now Mearls and his team are sifting data for additional ways to improve the game. No, they didn't shove a new system down anyone's throat. It was a very different feel this time around.
Two:
I think you believe the magic system in 4e was broken and that it was the "main problem" with 4e and that they "fixed it" in 5e. This is of course personal preference and not empirical data. Perhaps its fair to guess that many people didn't like that about 4e, but it wasn't broken - it worked just fine for me when I ran a game with it for 5ish years.
I'm stating this because what you wrote very much reads like "4e was broken and I'm glad they fixed what was broken about it when they made 5e" when it should really read more like "the stuff in 4e that was a deal breaker for me was removed/changed in 5e, which is awesome because it means 5e doesn't have that thing I don't like in it."
Or in other words, as I stated earlier, neither system is better, its just about which one you like more and that's all there is to it.
It was broken enough that I would bet money it was number two reason the D&D player base was splintered with the number one reason being the OGL. As I've stated many times, I would not release another OGL if I were WotC. It opens to many doors. I would instead create a friendly licensing agreement with particular companies to focus on aspects of the game like adventure design that a smaller company can do well and that encourages the sale of your core rules.
I'd love to see how many players fled D&D solely because of the magic system. If that number is high, that is a system that failed to attract a huge part of their customer base. I get it. There is a loud minority that wanted to see casters taken down. Even I admit they needed to be taken down some from their insane 3E heights, but not as low as 4E took them. Magic is powerful. It's users should exceed the power of mundane weapon use or martial maneuvering, even if you have two demigods: one a martial, one a caster, the caster demigod should have more breadth of power even if not greater killing power. That is a major part of the fantasy genre.
The nice thing about 5E is you can make casters of varying power and versatility in all areas. Or martials of varying power along the caster-martial curve. It's very versatile, even more so than 3E.