@Megas
As I mentioned, I pretty much only use Gladius vs frigates, mostly just in early game. Or put in another way, I mostly just use them with Destroyer carriers, which aren't so OP starved.
As for Thunder vs Gladius, replacement rate is more crucial when you have a smaller fighter swarm, and Gladius has much better dps vs shields. The faster my fighters can remove shields, the faster I can blow things up with HE missiles. I rather use Thunder for their interceptor role. Their overall shield dps is much lower. I haven't done the math but I daresay Gladius will at the very least also be competitive when it comes to armor dps. Gladius also wins with hull dps as well. Given that, the Gladius is the obvious winner when it comes to dps. Thunders' strengths are in the department of utility. ie: max speed, engagement range, and EMP damage, and I use them as such. I agree, the swarmers are good for distracting PD, but they're absolutely nowhere near as effective as decoy flares. To approach that level of use you have to have a substantial swarm of Talons constantly peppering the target with swarmers, and even then it only distracts PD, not normal weapons or missiles.
Broadsword, at first glance, seems better than Gladius in every way but the mobility of Gladius grants it hidden stats, so to say. They reach the target faster, they can stay in range faster, and can turn faster to keep their guns firing more often. In that way, a single Gladius is able to output more dps with the LMGs alone than the Broadsword. Add on the IR Pulse Laser and Gladius easily outdoes the Broadsword in that department.
Availability is irrelevant in ranking fighters. You use whatever is available + whatever you can afford + whatever is currently best. It'd be silly to skip a better option that's currently available just because it's not commonly available. It'd be like skipping on a Tempest, Paragon or Astral that popped up in the market or had a chance to recover just because it's a rare find. Where's the sense in that? If it's rare and it's good, buy it when it finally does pop up!
@Igncom1
The class is just their intended design/use. You can use any ship for whatever use you like, of course.
As far as terminology, fighters are just that. They fight things out with the enemy, ie; going toe-to-toe. 'Heavy' just means beefier. Interceptors are meant to intercept, ie: super speedy, long ranged, and capable of disabling dangers. North America, for example, invests heavily in interceptors because of the huge area it has to protect from several directions, and has to deal with very speedy potential dangers like intercontinental ballistic missiles.
That doesn't mean that interceptors can't engage in other circumstances, however.
Fighters don't necessarily need to be tanks, they just need to win. But I disagree with you; the Gladius is quite tanky. It is faster and more maneuvrable, ie: harder to hit, and it has decoy flares which decreases the effects of any attacks. Sort of like what armor/hull does, no? It just doesn't have as much hull as the Broadsword, which is a fair exchange for the difference in maneuvreability.