Only speculating about your and that FdL build, and the capability of the FdL pilot:
- your prismatics give you, without any other support (which you didn't mention) ~1100 MJ raw protection
- three (1 H, 2 M) focussed PAs will deal 55 SDPS raw damage up to 2 km range. 1100/55 is 20 seconds
- assuming beams on your side, an OC'ed H will give you 55 SDPS - up to 600 m range, with a maximum range of 3 km. The two unmodified (again, you didn't mention anything) L beams will add another 40 DPS to that, for a total of 100 SDPS - at 600 m range. If the FdL went all-in for shield tanking with Prismatics and Guardian boosters (you didn't mention them using SCBs), that'd mean ~6200 MJ thermal protection (for a balanced shield - thermal focussed could be larger).
- an FdL is agile, that's the point, and a good pilot will control the engagement distance. If the FdL kept the distance at ~2 km, that means he could deal full damage to you, but you would only deal ~10% of your max damage to him, so you're left with maybe 10 SDPS against his shields. During the 20 seconds he needed to take your shields down, you would have dealt then ~200 MJ worth of purely thermal damage, less than 5% of his shield strength.
- after your shields have dropped, a Grom missile would prevent you from jumping out (I just hope these Grom bombs don't work against shielded ships, I got no experience with them)
- if he's good and can hit it, three shots from a huge focussed PA are sufficient to punch through the hull and take out a Cutter's power plant
Did anyone mention yet that size isn't everything?
No1 in their right mind is using focused PA's on a FDL, but yeah, there's nothing in what the OP described suggesting a cheat.
If you're already into damage calculations, the per shot damage of 5 efficient PA's is more than 400. It will be more than 600 with fully proc'd thermal conduit. Even more if there are some SRB PA's in the mix.
And if it was a good old plasmaram, the damage could easily have been more than 1000.