Flagship Paragon is more dangerous than flagship Onslaught.
Strongly disagree. A flagship Paragon is too slow and doesn't have the range - aside from its lances which don't do hard flux and are easily dodged or blocked by other enemy ships. It may be harder to kill with reaper swarm, but it's much less dangerous, and it's much easier to kill with long range non-missile weapons. Essentially any decent cruiser can take down a Paragon - I wouldn't hesitate to engage one with even just a Falcon, let alone the stronger cruisers like Eagle, Apogee, or Dominator.
A flagship Onslaught, by contrast, has superior range and mobility; it is difficult to disengage and vent flux, and the Onslaught is durable enough that - reaper spam from an Aurora or Doom aside - you need to lure it into making multiple mistakes before you can take it out. It is
possible to kill one one-on-one with a Dominator (or Eagle or Apogee, though the Apogee would be especially difficult due to its lack of a mobility system), but you need to play absolutely perfectly; any mistake and the Onslaught will just rip you to pieces.