Valve's balance philosophy right now is that if everyone uses something, it should be changed. You can see it with CSGO. You can see it in earlier TF2 weapon balances.
The difference is, the CSGO was community will abuse a weapon to hell if it's OP, forcing valve to take a look at it. This happened with the CZ-75a. People complained that it was OP, to which Valve replied "prove it at Dreamhack."
In TF2, we just ban it and move on. Comp TF2 players want to stick to as close as possible to release mechanics. Release TF2 was a crafted experience that rewarded getting better with easily predictable and readable player silhouettes. CSGO is too: All guns have distinct ways to tell apart, and you can (within reason) predict what a team will run if you keep track of the economy. Which leads me to the point:
gr8stalinThe instant the Sandman made it into TF2 was the day he lost his credibility regarding TF2 as it was a direct violation of the established design philosophy regarding TF2 before the Scout update.
Valve fucked up.
While CSGO may have added new weapons and mechanics that weren't present in previous titles, Valve made sure to work with pros so that nothing in the game broke the CS design philosophy, which wasn't even Valve's doing in the first place.
With TF2, Valve carelessly added new weapons and mechanics that go against the carefully balanced game that they set out to create after 9 years of development. After 7 more years, they've fucked up too hard to go back on the decisions they've made. The game is chaotic and unpredictable in a setting that allows all of the weapons to be utilized. They want to address this, but they run into the problems that A. No one in Comp play wants to use these weapons and B. No one wants to work on TF2.
I've largely given up on anything coming out of Valve regarding properly balancing TF2. The only hope for that is either a TF3 (as any changes to TF2 will anger the large majority pub population), or a standalone game of someone else's making (people have been looking at Overwatch), and maybe it's time for that.
TF2 has had a 7-year life so far. It's natural for players to just lose interest. Dedicated players will still play and have fun. For instance: the arena shooter scene never really died, dedicated players keep playing as long as they enjoy it. No one in #uscpmpickup is complaining about how there's literally zero developer support for Quake 3, they just play their game. A couple brave souls wanted the arena shooter scene to propser again, so they started Reflex.
If you want TF2 to stay alive, just keep playing it. If you want it to grow, make your own game, because Valve won't.