The way sirens stack is the problem.
I don't think too many has problem with the additional movement speed, it's all about how BADLY it's implemented.
I personally think there is TOO many anchors already in the game, but atleast it's somewhat balanced.
You could very easily just put a limit on the bonus and put ranges of the bonuses, if they are so stubborn to add multiple new anchors.
1-19 sirens - 20% bonus, 20-49 40% bonus, 50+ 60% bonus etc.
Even if I think it's by far best to have a set bonus and don't stack them, which by itself is really good already but not game-breaking like now.
If the dev team don't understand from start how 50 possible re-timings is bad.. Then we are really doomed and I'm afraid what is waiting for us in the future. You might as well just remove the anti-timing all together at this point.(Don't take it as a suggestion.......)
I gave it a shot with a open mind to see if my initial worries were unwarranted.
And....It was even more game-breaking then I were afraid it would be. Not even a challenge anymore to do perfect timings.
And I'm not even a top-tier player, hell some would argue I might not even be a decent one even.
Personally I won't touch any Aphrodite enabled server until this mess is sorted. As my last hope in the devs is they don't allow something as this broken.