My base defence mission was a real PITA. I got a MEC, 2 supports, an assault and a sniper. Carapace armour, laser rifles (the sniper just had basic armour and basic rifle). The cyberdisks (4, with 2 drones) I fended off nicely. The chrysalids weren't a problem. The mech bay seemed to be an ideal defence position: elevation, cover and a (mostly) unobstructed view of a large area, with nice funelling areas which allowed for some nice murder zones.
Only, the enemy threw 4 mechtoids at me. Four. I didn't know those blighters could fire twice if they remained stationary. Couple that with a few berserkers (harmless if you can down them fast enough) and some mutons ... The base defense rookies got some nice kills, but panicked nearly every single time. My regular troopers weren't exactly high level (screwed up the last mission, losing me nearly a full squad) and in the end, one assault soldier made it out. I promptly gave her all the medals, all the gear and spent ALL my meld on getting her kitted out with genemods. She's a beast now, having fought off 3 sectoid commanders and a few heavy floaters single-handedly during a landed UFO operation.
It was an absolute nightmare of a mission, a close-run affair until the very end. I'm not the greatest tactician, but boy, it made me sweat. This was on Normal / Ironman too. The game has gotten harder with all the new toys. But, as always, if you delay doing missions, you will find that the game throws bigger and badder meanies at you. Four mechtoids is nothing to sneeze at, especially if the AI is smart enough to keep a sectoid in heavy cover and far away from the frontlines. Those mechtoid shields, man ...