This topic already came up a couple of times I think.
As I understand it, there are actually 2 versions of the precursor ranger you can find.
One is simply a mid-level dreadnought similar to what you could build at this tech-level, i.e. not all that powerful.
That would be the "standard" random event.
And then there's the mega-event version, what is what you got.
This one is extremely powerful, similar to the ships you get late in the ToA campaign.
Early in the game, those mega-event rangers can be effectively game-braking, as there is not very much you can do about it.