That very agency seemingly takes the money from the user of the photos, not the photographer.
One can say so !
Example : You as a photograper will state : My earnings for 8 hours of work for this job have to be
between 800 - 1200€ it depents to further circumstances and client has to pay for!
Then you have to find a client who is willing to pay and not to state : I (the client) have 3 photograpers who will do the same job between 450 - 620,-€......

!
Bad luck for the client I would answer

!
But (if your reputation is good enough [what is not identical with : you are better - in some cases]
The right agency will bring you in contact with clients who normally pay much much more (2200 - 4500,- [and above....

]
Better to say (in often cases) the agency will bring the right clients in contact with their best photographers!
And if here the more money you will earn is in parts to the agency is quite normal and quite OK!
Of course one can say so : It is payed from the clients (the money the agency get for its
"support"!
Well what is not OK (for me) - what is unfaire business?
The case that you as a photographer have build up reputation AND contact by yourself (without any help) but then your client want to work with an agency! There is coming a trainee from the agency (without any knowlege) and is telling you as a photographer how to work

!
And you are told wrong (from wrong background) - at least the agency get payed from the client and you get suddenly paied via an agency

!
Soo you are " feeding" unprofessional trainees from who you are told wrong

!!!?
But that is more the ",modern " way with special agencys (advertisement a.s.o.)
The final (basis) decision is therfore in regard of the following question :
I am advancing a photographers agent with my work or is a photographers agent advancing me?
The perfect middleway is that both (to same parts) get in advance!
But that will allways imply that you are "partners" from same reputation! (same excellence in profession)
with regards