Honest, my gut reaction reading this was "it's a load of horsecrap". But I'll try to be a bit more constructive than that.
I'll start with the one point where I agree: yes, if you're enjoying a single champ with a single specific playstyle, you've no guarantee that they'll keep the same for a long time. And yes, even though it's not my case, I do understand that it's painful and frustrating. That would actually be a reason for me to leave the game.
But you don't HAVE TO main a single champ with a single playstyle. You can main a same champ through different meta and adapt to different playstyles. Even something as simple as Garen of all things has gone through 3 or 4 main builds over the last 2 years, and it can be fun exploring and learning even after hundreds of games on a champ. It can also be fun exploring and innovating and beating people thanks to your innovation. Things changing is not necessarily a negative.
And things changing doesn't mean your "investment is flushed down the drain", that's just a plain, gross exaggeration. If the build you mained is nerfed or fall out of flavor, there is still another build taking its place, and as a main of your champion, you should have a much easier time adapting to it than someone who's just trying to pick up the new flavor of the month.
Likewise if it's the champion who's affected instead of the build. If you played a Juggernaut or an ADC or a Burst Mage to hell and back, even if they are reworked and you don't enjoy them anymore, you should have an easy time picking up another Juggernaut, ADC or Burst Mage that you enjoy more and that you'll learn pretty quickly based on your experience with similar champs.
And on top of all that, whatever the champ you're playing, LoL strategies and macro-play principles always stay the same, and if you master it, it will stay with you no matter what champ you end up picking. Saying that LoL 8.10 is to LoL 5.7 or whatever what checkers is to chess is a ridiculous analogy. The details change all the time, but the core of the game is always the same.
Also, the game wasn't changing as much in S4 / S5? That's rose-tainted glasses right there, you might wanna re-read the Patch notes of that time. I barely had learned the S4 Jungle that it changed all over again in S5. The game was always changing.
EDIT: oh and what's that comment about chat even mean? Like, that's the biggest crap of it all...