I don't agree. Generally it's very simple, until you defeat a jellyfish in space (one on one) I don't accept other arguments.
I'm still not sure what the Thargoid argument has to do with anything. Killing interceptors one on one, no matter how easy or difficult, is not going to make someone better at fighting CMDRs in large ships than fighting CMDRs in large ships, which has been done since long before and after Thargoids.
The issue isn't that from a big ship they shoot frags, the issue is that from a medium to big ship they shoot frags.
Medium ships with frags still have to contend with all those other medium ships and frags are much harder to leverage against opponents with parity in mobility. This is a key balancing factor to frags that you're dismissing. The entire population of PvP pilots isn't suddenly going to focus on hunting the minority of big ships to the exclusion of everything else.
That's what I'm writing about, no one else will fly in the open game on big ships and those who will fly there will be on medium-sized ships with frags.
That's not a likely scenario.
Firstly, some pilots being able to leverage the extra ~20% frag DPS a Python Mk II is capable of (relative to all the other medium combat ships capable of mounting frags) is not going to suddenly make the game dramatically more difficult for large ships than it already was.
Secondly, not everyone is going to be boating frags because frags aren't good at everything. They will see a resurgence in popularity, for a while, as people experiment with the shiny new ship that seems to favor them, but when people adapt to this temporary increase in frag popularity, and realize that frags suck a lot of the time, loadouts will diversify again.
The game has tons of balance problems, but frags barely register. The problem with big ships has always been one of mobility and that problem exists without frags. Mobility is handy enough alone, but it's a huge force multiplier in groups, especially well coordinated ones.