Well... thing is, the Imperial grav tanks are only 15 Td, not frightfully expensive, double as slow-but-very-deadly air/space fighters, and are not normally fielded where the locals exhibit no will to live nor technological parity.
1st nuke dropped gets the firer dumped on with a handful of nukes on the launcher. Followed by promises of saturation bombardment if another is dropped. And if another is, the combined meson and nuke fire takes out the ability to hide or fight, right after whatever is left bugs out.
As for missile saturation... it's not quite as easy as it looks, especially if there's a TL difference. Striker doesn't present the whole picture, but basically, the Trepida squadron includes a same speed Astrin-E ECM platform... which can jam and spoof missiles pretty well. It's not assured defense, but coupled with on-trepida PD capabilities, it's usually good enough. And the Trepida isn't heavy armored (only 40 - same as a starship), but it is mach-1... many tac missiles won't catch it, and it's orbit capable. And only MCr20... it's job is to protect deploying marines, not to be a MBT. And in that role, it's a wonderful boat.
Unless you're the poor schmuck assigned to one. Then it's a hot shakey ride straight into hell at mach 1+ as you fly with the drop troops. And you pray that the big boys got all the big PlanDef with Mesons from orbit. And that the Driver stops before you smoking hole.
in modern present day parlance its a HIND-D on heavy Steroids and unlimited on station time.