Tiers are not necessary to keep the game alive, I dont know how many people already said thats precisely the reason they left world of tanks and similiar games.
I understand it might be some people play to get the next unlock and unlocking new gear is fine. Just dont limit us as much as a Tier system does.
You have to concentrate on one ship class to keep up with the grind or your friends will have to play "low tier" to play with you, slowing them down in the grind.
Since you have to concentrate on one ship you can only play that ship, no more selecting the ship that benefits your team/friends unless you only play low tier.
You have to fight against stronger ships (higher Tier) in certain matches giving you a disadvantage because you grind less.
You cant just join and play with people who started playing the game before you like it is now.
You cant freely pick a ship you want to fly due to the grind.