Flak/merc Spire is awesome against a ramming Pyramidion. If you know they're coming, you've got plenty of time to take them down, and if you know how, you can kite backwards and drop mines. They either have to turn to avoid the mines which severely decreases their speed, slow to a stop, hit a mine which will knock them out of trajectory, or rise and elevate, but a good miner can make a pretty effective wall. I had my doubts at first, but it works incredibly well.