As far as I can tell from farming Remnants for a while, there are two things that are "problematic" about the Radiant. I use the quotes because neither of these actually has to do with the ship itself.
Problem 1: Other Remnant ships are not threatening enough, so it feels like a large difficulty spike whenever the Radiant is around. Personal opinion: endgame fights should be challenging, so when the source of frustration is that their difficulty is inconsistent, the solution would be to buff other Remnant ships.
Problem 2: The AI seems particularly bad at dealing with the Radiant. It neither aggressively finishes the ship off when the ship is retreating unless the player intervenes, leading to Radiants with a sliver of hull remaining being allowed to retreat, recuperate, and return to decimate the fleet with their strong shields back up, nor is it wary of the swarm of Reaper torpedos that the Radiant can unleash at all - or at least the impression is constantly that the AI is not especially careful about them, so rather than avoiding impossible fights, tends to engage Radiant in presence of other ships, lose the flux war, and die to a swarm of Reapers, in a way that seems particularly stupid and frustrating from the player's perspective who will of course see that the enemy ship is menacing with Reaper launchers and that it is particularly important not to be in a position where you will lose the flux war against it. Again, though, this is a problem with the AI or even especially with player perceptions of what the AI should do rather than the Radiant; it should be fine to have agile ships with bursty damage. So the AI is either too cautious, or not cautious enough, depending on context, which of course seems like a slightly hard problem to correct. The latter "issue" could likely be partially fixed by just reducing the missile slots on the Radiant, buffing it otherwise to compensate, to make the deaths seem less stupid to the player. The former "issue" maybe by shifting its defenses more towards armor or, say, reducing shield arc or something to avoid the near-dead-Radiants still being entirely capable of killing everybody issue.