I'm not sure I've ever encountered the Precursor Ranger in 4 years of playing this game on and off, certainly not in the hands of the AI, so I don't think it's all that common (although different players seem to encounter different events more or less frequently). The player can get them too I think, again quite rarely, I think I have seen it mentioned in forum posts in the past.

To defend against it - if you can convince the Terrans to make peace and then dig in and research for a while, you may in a while be able to swarm it with ships that overwhelm it eventually - and if you bribe someone else to attack them they'll probably send the ship off and you may never see it again (especially if this stronger version is still slow, as I remember the weaker Lucky Rangers being). Usually if I encounter one of the events where there's a vastly powerful new opponent (have you encountered the Mega Pirates or Peacekeepers yet?) this is what I have to do, until I can build ships that can fight back.

My last game, the AI received FIVE Precursor Rangers, the Yor got two of them and the others were traded around until finally I bought three of them.

Usually of course, it's given to the races which are lagging behind badly on Military.

My enemies do get the Precursor Ranger rarely. Most of the time, I manage to obtain them one way or another.

All in all, only three of my games did the enemy kept the ship. And in all three times, they blew up.

One time is when the Peacekeepers showed up and their Precursor Ranger went down in a hurry.

The second time, I manage to catch it alone and, since it is nearly the end of the game with late-game technologies, I manage to crush it with my Revenge Fleet!

The third time, it was in a fleet. But since my Industrial Output was far superior, I built several fleets of 6 battleships that was heavily armed and shielded and sent them against the enemy, They did win against the Precursor Ranger, even with losses.

Not always though. During my previous game, the Krynn, who controlled 80% of the galaxy and had a military at least 5 times the remaining two races combined (the Altarians and my hamstrung Yor) received not one, but two precursor rangers, the Alterians received nothing and I received two crappy Lucky Rangers (that came nowhere near the PreCursor Ship) before eventually receiving my own PreCursor Ranger (which was then swiftly blown up because by then its lead on the rest of the galaxy wasn't that impressive).

I didn't mind though. It greatly added to the general feel of the game (OMG I'm gonna die against this ultimate enemy!), and made the end even more of a climactic turn-around. ^^

I've had precursor corvettes and the precursor rangers and have been on the recieveing end as well.I've conquered entire galaxies with a ranger and had my entire armada wiped out by one solitary ranger.The AI tend to get rid of their Rangers especially if their draining their coffers their on easier settings.

I normally get 1-2 fleets of precursor corvettes per game and as for Rangers can range from none to each race having loads each.I once played a "normal" game against 9 opponents and got my arse handed to me as all the other races got 3-5 rangers each and used them to wipe my empire of the map.

Another tactic involves speed.

As one commenter said, if you get the enemy chasing one target, just lead it off and around and around.  Just take care not to get more than two extra squares away or else it might reset its target.

If the enemy sends transports in its wake, you need faster ships with just enough attack/defense to pick off the transports as they come.  This is similar to how one can deal with the DreadLords, buying time. If the AI embeds the transports in decent fleets, then you have another problem.  There is an exploit to deal with even that, but it is too gamey to be shared in polite company.

HighWater is correct, and the suicidal deepstrike is fun, especially at Suicidal when the AI has all the other cards.

One can, for example, sort through the enemy planets to find where they have things like the soldier training bonus facility, the aphrodisiac trade good, the eco capitol, etc and target them specifically.  If one spots re-invasion transports in-bound that cannot be stopped, one can raze the bonus facilities or even destroy the entire colony - - relegating it to a PQ 0 planet.

I have yet to test if, once a bonus facility is destroyed in the above fashion, if I can now build it myself within my empire (like the soldier training one).  I think I have done it, but cannot now recall for sure.

It allows a bit of scope for role-playing.

Remember, also, that the first step is taking out the enemy anomaly mining bases!

In DA, the MCC is a conundrum.  It gives a 100% eco bonus, so you do NOT want the enemy to have it.  OTOH, if stops planet-flipping (a known DA bug).  One "solution" I have adopted is to take it away from an AI, let my treasury build, evacuate the planet down to 1 colonist unit, then gift it to another AI, preferably an ally or a minor.  The low population makes the game engine value the planet low, so I can always buy it back with tech later if I need a fresh cash infusion but, in the meanwhile, I flip some more planets.

Bribe someone else to war against the Terran.