This all sounds like players blowing things out of proportion as usual. I personally fail to see how it's now suddenly 'pointless' to increase military bonuses just because the enemy boosts have been adjusted. It was more pointless to raise attack back when the strongest armies we faced were in GE, not even going up to 300% boost. People still increased their bonuses even back then, so why is this adjustment suddenly making all of that worthless? Have some perspective, people!
It's pointless in the other direction. Because of just how hard they scale it up in a hurry, there's really no difference whether you have enough boost to beat 800% or enough boost to beat 1600%. You're basically making the exact same contribution because of how fast it moves between those two values. This was true under the old system too but if you managed to clear 1750% you suddenly got good value so at least there was a payoff at some point. This was probably the wrong way to go about it, but still better than no payoff because it'll now rapidly climb to 2500% to 3000%, etc. Furthermore all value of attack boost are lower than being a half-decent negotiator despite being a world of difference in terms of setup.
As for why people kept investing in boost all these years: Because some people are more interested than others in just investing to seeing bigger numbers. At one point attack boost was crucially important, and they just kept going because that was the number they decided mattered to them. Some still will, sure. It doesn't mean it has practical value. If you've got enough boost to fight to the end of GE4 in mars, you've got enough boost to take minimal losses for most of the fights you can do and to hit the steep region where extra boost doesn't matter much anyways as it'll only be a few more fights for a *ton* of city space.
And I do have some perspective - I quit once because of a lack of a real endgame. I came back because GBG was that real endgame. Apparently though, it's going to railroad people who want to use it as an endgame to optimize for into treasury goods for siege camps and/or personal goods for negotiation, because boost is irrelevant past a point due to the shape of the attrition curve and troop count is irrelevant because you'll be stopped by boost first. Furthermore, I'd expect additional changes to curtail those options eventually, because "it's not supposed to be a play all day feature" and they're both able to stretch out how much contribution you can make greatly over fighting. At which point we'll be back where we started with nothing worth optimizing for at all and the only appeal to people at endgame is those who either want to play farmville and show off a pretty city or play FP simulator and see how far they can level GBs they don't need. Yes yes, lots of people do that and enjoy it. I don't.