MAKE MIDDLE ROUTE NINJA GOOD
Maybe I'm just a BTD6 noob (which wouldn't surprise me, I have trouble doing C.H.I.M.P.S. on any map), but Middle route ninja sucks. Bad.
Its supposed to be the Support Route for the Ninja, both buffing other ninjas, erasing camo, pushing bloons back, and that's all fine. Its when you get to T4 and T5 that it really starts to suck for me. 5K (on hard) to slow down all bloons for 15 seconds, and then a 60 sec cooldown when you can just get a glue gunner and ice monkey feels so out of place (I get they stack, but still), just doesn't have nearly the same impact as T4 top and bottom route.
Then T5 buffs the duration to 30 sec, buffs shinobis, and damages newly-spawned MOAB classes. Its not bad for a T5 under 30K, but I feel like people only get 0-5-0 and even 0-4-0 Ninja monkeys IF they're going for a Ninja heavy build.
Here's what I think is a decent buff for T4 and T5 middle route Ninja monkeys
For T4, make them count as a 3-stack of Shinobi Tactics to other Ninjas. Not only does this give a reason for making more Middle routes past Shinobi Tactics, but it would also make it much easier for Ninjas to reach higher Shinobi multipliers due to how much less space it takes up. Secondly, it can keep the 15 second ability with a 60 second cooldown, and it keep the slow down, but it could also slow down bloon spawns. The original name was, "Sabotage Supply lines," it makes sense that bloons would spawn slower. That's optional, but I think the 3x shinobi stack is a good idea, at least on my end.
For T5, the sabotage should be permanent, end of question. It should not be as powerful, sure (maybe an 80% slowdown instead of a 50%, and a 10% damage to MOABs then a 25%), but as I said earlier, Grand Saboteur is a T5 that is nowhere near as good as the other T5 Ninjas, even if they are cheaper. Instead, while it has that passive, it also has an ability that changes the passive into its usual 50% slowdown and 25% damage for 30 seconds like usual, as well as buff ALL NINJAS, not just SHINOBIS. You're not going to be using Shinobis for damage, even if they're likely to have the most shinobi buffs considering how stacked up they usually are. You're using the top and bottom routes for damage, so instead of restricting the buff to just Middle route ninjas, just do it to all Ninjas!
Maybe I'm crazy, and there would definitely need to be some price adjustments, but I just feel like Middle route is just nowhere near as impactful as the other routes, yet it definitely has my favorite art of ALL the ninjas.