My first suggestion is halve the build time (or eliminate it altogether). Unlike building defenses and guns and things, you shouldn’t be interrupted while building rallies (if you’re doing it right), so the build-speed isn’t really a factor in the “strategy” of it all, it’s JUST an annoyance that takes you out of the game. Since you can only have 1 up at once it’s not like you can spam them if they speed up the build time.
If it’s that easy, more people should have it up.
Maybe lock all other engineer buildables behind the rally, as in, if you don’t have an active rally you can’t build anything EXCEPT a rally until you do.
Maybe increase points, again, for building and for people spawning on them.
Also, make them harder to kill, they should require explosives or sloooooow un-building like hedgehogs, so not every single soldier in every circumstance can take them out. Would mean the rallies that DO get built will stay up longer.
I don’t think the solution is to take people who do build them (me) out of the game for longer to toil in the rally factory. It’s not just the build time. I can’t be in multiple places at once, so setting up 3 flanking rallies by myself, that means I’m gonna get my first kill 2 minutes into the game after running hither and yon and then hammer, hammer, hammer, hammer, and pretty soon you’ve actually made the problem worse, because i get fed up with STILL being the only one with rallies up, and i stop building them altogether.
Ultimately i think the quickest solutions that will yield immediate results, if meager ones, would be to increase the points per spawn, and make rallies harder to destroy.