I think some more info on what buffs overwrite each other, and their actual bonuses, in tooltips would be useful, and also I would think that either ZSTMs should work in a system with a drill, but assuming it currently doubles move speed of allied ships, then it would allow allied ships to move at a rate of 16. Also, possibly improve the galaxy pathing to take into account not only enemy planets and number of jumps, but also distance between wormholes and the effects of planetwide speed modifiers. That way, your ships would tend to bypass Gravity drill planets, and prefer routing through planets with ZSTMs
mostly unrelated, I think that Group move should be applied after speed bonuses, rather than before, as In my current play through of LOTS, The shards happen to not gain speed boosts from ZSTMs, so my fleet, and especially my Shield bearers, are all pulling ahead of the shard, which is annoying, because I cannot use group move in that case.