In 1.301, the AI logic against exo-shields was fixed. That was my takeaway from this post, not that it helps against infiltrators. If you are commonly going up against massive infiltrator waves, I'd suggest some combination of tractor beams, gravitational turrets, MLRS turrets (or other multi-shot ships, like starships), and/or snipers/spiders. I was facing down waves of 3k-5k mark II infiltrators in my game the other week, and it was fine. We lost some planets, which was expected with that volume given how our defenses were, but it wasn't game-ending.