You are right to a point, but small gang to me IS 3-4 people and the cyclone has the same problems as the Myrm as number increase as do all active tanking hulls. Also...
There is no 'cyclones can just roll shieldgank' because there is no reason to fly it like that- because you can fly a Hurricane. Even issues of isk are irrelevant because anyone that can afford a cyclone can afford a Hurricane and those that dont know better or dont have the skills to fly a BC yet, well there is no helping them and it doesn't matter what they fly anyway.
Myrm/Cyclone niche is high output active tanking on a BC hull. In that niche the Myrm is better.
You say tripple rep caps out fast. So does Cyclone Xl booster fit. The difference is, the Myrm can choose to have only 2 reps active where the 3rd is redundant and you are able to micromanage cap and use your reps more effectively- no risk of 'overrepping' and your more evenly distributed rep cycles are better for a sustained tank. You can also carry dual medium boosters and tackle, something the Cyclone most definitely cannot do. If you want to get really nitty gritty, the Myrm can also carry a flight of ewar drones for GTFO of dodge moments, the cyclones DPS is low enough already it cant afford to love its 3 medium/2 light drone flight.