Ok, just checked this out after hearing about the "flea issue". However, I think I can say that the reason that jumpy lost here had nothing to do with fleas. It seems clear to me that it was the 520 metal floated by trying out a strat to optimize wind energy without building solars. And unfortunately, this being the smallest map I've seen in the game so far, makes it vulnerable to rushes - which did come, and did throw a wrench into the build order.

That being said, there is a 10-second segment to pay attention to where an approximately equal amount of metal in fleas goes toe-to-toe with a pyro, which is surprising - at least to me. (and which we could just do simple tests to try to replicate) However, it did seem to me like Godde had just used target fire on the burrowed fleas. So perhaps it was still aiming at an empty piece of ground when the fleas charged? If that's true, maybe the lesson might then just be to keep pyros on free-fire when near flea balls, and not try to risk smoking them out and have them wake up and eat your face off.

(also, ideally, I'd love to be able to have a "target fire", that when targeted on the ground would fire on the spot only if there were no enemies in range, but switch to free-fire when enemies appear)

So Fleas are faster than the Pyro, and can beat single Pyros in defense.
Add to that that Pyros suck against Lotus and the spider player can just harass all jumpbot expansions, force the Pyros to run around and force the Jumpbot player to make defenses to secure expansion. Meanwhile, ambushing Fleas will beat lone Pyros, it is not to hard to keep track of the enemy Pyros and making defense where the Spider player see fit.

A line of Pyros is very cost effective against other raiders if you just retreat them and repair them before they die.
Edit: That requires quite a bit of micro though.

Well what squishy units are you trying to protect? Moderators? Firewalker?
Just go ahead a little of your squishy units. Just 300-500 elmo is plenty especially since the Moderators and Firewalkers should have turned and started to retreat aswell, effectively letting you kite longer before the enemy raiders reach them.
Also Firewalker should restrict the angles from which enemy raiders can approach without burning. If the raiders bunch up, they will suffer even more against a potential Firewalker salvo and Pyros.