Yes it's a completely different game on high difficulty levels.
Here's a newer save file. I had triggered 2 Raid Engines and both of them sent about 7000 ships. There's still about 5000 AI ships on SHC-106.
I don't need a huge fleet since I ignore most of the AI planets with Assault Transports and only do surgical strikes and beachheading. Which is also why I haven't bothered dropping Warp Jammers on those neutered planets. I don't care if the surrounding planets get reinforcements since I'm just going to fly past them. It would be just pain in the ass rebuilding the Warp Jammers every time there's a big AI threat fleet.
I don't have higher Marks of Metal Harvesters unlocked because I chose Mark III Economical Command Stations.
Not all of my tech unlocks are defenses. I have unlocked Mark IIs of Munitions Boosters, Neinzul Tigers, Engineers, Cloaker Starships, Scout Starships and Enclave Starships. In addition to that I have Assault Transports, Mobile Space Docks, Warp Jammers and Mark III Economical Command Stations.
And the warheads on my home planet aren't nukes. I
am going to use 1 Mark II Nuke later in the game however
Possibly also some Mark Is. Anyway the warheads on my home planet are Lightning and Armored Warheads. I'm stockpiling full caps of all of them. I mostly use them to stop CPAs. Normal waves are usually stopped by defenses. I will be using
a lot of Warheads when I attack the AI Homeworlds. They will be used to destroy the Guard Posts and to get rid of the Strategic Reserve. That's when the higher Marks of Cloaker Starships kick in.