You litterally don't need your exact number to know if you perform well. You just need to know you do your job well and again, dummy if needed "Stone, Sky, Sea" if really concerned. Simple as that.
As far as I am aware they ban them in batch from time to time, so you are right here, they don't do it all the time unfortunately.
The writter's own claim? Not good enough for you? Maybe you know how well it works better from the people that write the tool, I don't know... You can send me video of you playing without DPS meter, or even battle logs on the screen, I will tell you how good/bad you perform and if I am wrong, we agree that you don't get any info except your meter.
But let me explain you how you ACT works (obviously you have no idea). It takes the info from the logs and use formulas to simulate expected behavior, for example the dots of the summoner were entirely simulated in the meter, so their accuracy may be pretty good sometimes and totally on another planet other times. Same goes with buffs/debuffs, There is no info like "dragoon did 10 000dmg +1 000 trick attack dmg. All of this info is simulated by the ACT too. If you care about your personal performance, I will say it again, if you want to perform well, simple math (with no numbers involved)
Resource overcap = bad performance
CD stay unused = bad performance
Use weak abilities when you have stronger options = bad performance
OGCD skills in GCD window = bad, just don't.
Avoid the four mistakes I just said, you are ma' man, I don't need numbers to know it!!!
Things that ACT have no idea of, but they actually improve performance of players quite a lot are proper usage of Feint (many people claim you should eat food for survivabily instead of using this really cool skill), bloodbath, second wind, shade shift, revives from red mages and the list goes on and on. Because wasting time of healers to heal you, or tanks to give you extra def is wasting the party's overall dps for the sake of you're missunderstanding of how the game works, just because you can't read tool tips, but just dps meter...
As I said, less groups were using it day one, more were using it day two, same for other addons too (that I believe are more likely to be the reason SE are angry).