How much of research you did? Have you flew all of them, had them at g5 and done PVP with them? I dont think so.
https://inara.cz/galaxy-experimentaleffects/
^
Have been familiar with all of these? Tons of options, but its not easy either use them in right way... it takes some experience to be able to utilize these to fullest. Once done, all ships I listed ealier, can be quite viable to deal with FDL's (but skill is required as well in order to do so).
Since min-maxed PVP in Elite is very similar to rock-paper-scissors, in other words, every bulid out there, can be countered by other one. And I assure you, its not like only there is FDL only and nothing else. Even most skilled FDL pilot will have hard time againt counter-bulid that was made against its own given if opponet knows what they doing and how use thier advantages.
If you dont belive this, how about this: Take your time and go and bulid meta g5 FDL then go these places: Deciat, San tu, shinratra or any active CG and try not to ever lose in PVP to anything else than other FDL's... Good luck especially against shieldless FAS or cheftians that are being "stomped" so hard as you sayin.
Then pls come back and tell all of us, that against FDL no other ship stand a chance.