As should already be obvious, the RNG aspect of mission scripts leads to very different approaches in the mid-game. But I'll just write this as an observation to highlight the potential differences depending on the RNG you get.
In my current game, the aliens have been very lazy with the invasion that was supposed to begin on Jan 1, 1999 midnight. It's May already, and I've only seen two very small UFOs. That's it. Luckily, the military shot down a couple of UFOs in 1998, and there have been at least three Chtonite Minibase assaults. So there have been plenty of access to engineers, navigators, leaders or medics to progress the research tree otherwise as well.
On the other hand, I got lucky to get MIB cover-up missions (2*5 % monthly chance) . Shooting down their transporters will eventually lead to retaliation missions and MIB Stealth Bombers, which each have a number of MIB troopers equipped with power suits and shock armors. Which you can grab if you stun them with Katapeltes Spiritus (the other means of capturing them alive and actually getting a usable armor are essentially useless). Dealing all of these MIBs gives you rather easy access to about a dozen powerful armors you would not have a chance of getting any time soon otherwise.
In my previous game, about this time I don't recall getting more than one good MIB mission so the access to good armors was very different.