Something bodies like the CMA often struggle to get is the "evidence of harm" which validates their concerns.
Your story is a real example of a competitor or business actor being harmed in precisely the way the CMA hypothesised. It's absolutely worth writing a response to them, explaining your story and what happened, and whether you support their proposed remedy.
Facebook and all their lobbyist friends will be submitting responses saying they entirely disagree and this action will cripple the digital economy and nobody will gain from it. You can explain how you are a rival in the ecosystem, and were actively harmed by their actions that the CMA has hypothesised could happen. Having people affected get in touch and do this can really help the CMA to justify standing firm with their findings in the face of the lobbyist doomsayers.
CMA = Competition and Markets Authority (a UK regulatory body)
https://en.wikipedia.org/wiki/Competition_and_Markets_Author...
Please take the effort to document this and write the CMA.
If you do, I'll send you $100. I know that's not much, but this is important and worth the effort.
You should. These kind of situations are exactly what they'll need to show to move this forward.