That said, I think you're correct about not being so concerned. If the symbiotic relationship was so exploitable, it'd probably be a great evolutionary advantage to do so. The signal being a sugar itself, as you note, doesn't surprise me.
By “definition” I meant “the rhizopine signaling pathway”, implying that no pathway → no symbiosis. Of course that signal insensitive strains or species can exist. It’s a symbiote and not a parasite, after all.
Bacteria evolve frighteningly quickly.
Excuse me, I'll just be over here laughing so hard I can't breathe.
In terms of how long it'll take: evolution is slow in terms of number of generations per organism, but it's relentless. The more widely any modification is deployed, the more interactions there are, and the quicker in terms of time some adaptation will occur; and, once an advantageous adaptation does occur in one place, seed dispersal will allow it to spread quickly.
As an example that I single out because I read about it recently in the delightful "Lives of weeds" by Cardina (https://www.cornellpress.cornell.edu/book/9781501759000/live...), the adaptations of plants to deal with the "irresistible" Round-Up pesticide are highly improbable, but there were trillions of chances, and so it didn't take long for them to develop; and, once developed, they spread very quickly.