There's a number of aspects to dealing with ancients. You can actually kill them off with equal or less fleet power and less techs. It requires manipulation of your fleets, both what they have equipped and what kind of ships you're using, as well as strategy.
So far, every game I've played, the ancients on console have fleets of about 100-120k. Generally 2-3 of said fleets. Usually 2 but I've seen some with 3. Difficulty doesn't seem to make a difference from my experience, but I haven't exactly taken notes just going from memory.
Most of the time you only need to be able to kill one of those fleets at a time. It is rare that the ancients actually combine them together or use them in unison. That means you don't need a 200+k fleet to take on an ancient 200k-ish fleet, you can go with half and just take the fleets one at a time.
Let them send a fleet at you first. You can get defence bonuses depending on what traditions you've acquired that will help the battle. The Harmony tree has a pretty sweet defence bonus. This reduces further the strength of the fleets you need to take them out. You also get the benefit of a station backing your ships up.
Finally, look at what their weapons are. If they are going hardcore on anti-shield weapons, then drop your shields and stack up your armour. Choose your own weapons for the battle you intend to fight. Will you be jumping on top of them or letting them jump on top of you, or will you be trying to hit them from a distance to do as much damage as possible before they get a shot off?
I have killed ancients who had 330k fleet power when I had only 140k-ish fleet power and was pathetic in research in comparison to them. I haven't always done it in a single war, but usually 2 is enough. Generally I use corvettes and battleships. A corvette swarm to distract and pick off damaged ships and soak up some fire, and a few battleship fleets raining down with Giga Cannons and Kinetic and Neutron Launchers from a distance. With good evasion, the corvettes tend to lose a lot of ships but not all that many, and they do a good job of letting the battleships hammer the enemy unimpeded.
