I still own Amigas, I have no qualms in using the downloaded ROMs since I could in theory rip them myself, so it doesn't feel like I'm committing any kind of offence (not a lawyer though).
System ROMs were protected copyrighted works well before the release of Amiga in 1985. See the case of Apple vs. clone maker Franklin:
https://en.wikipedia.org/wiki/Apple_Computer,_Inc._v._Frankl....
What you describe is piracy. Your other comment about legality having a "bad reputation among Amiga enthusiasts" makes it seem like the Amiga community is one of criminals. That is sheer madness.