The whole LFQW thing was never an issue for any of the games I played in, in any edition, for myself at least (and no one else every complained about it to my knowledge).Very much disagree with this. The scaling of spells led directly to the whole LFQW problems in earlier editions.
It wasn't until I started playing 5E and heard it mentioned here that I even learned of it! I actually had to google it to even find out what the heck people were complaining about LOL!
So, for the people who do/did take issue with it, that's fine. But for people like myself who never found it to be a problem, the idea of upcasting is harsh.
How many times have I heard people complain on these boards and in our own game about spells losing some of their value at higher levels? More than I can count or care to remember.
The answer, upcast.
The problem, then you can't use those slots for spells of those levels when you want to use them.
I think they could have had spells scale, even it it wasn't as powerful as earlier editions.