Sorry, I'm not quite following. Unbunching is not a feature of this mod, if that is the question? Unbunching is done by default by TP2, as far as I'm aware. Did you mean congestion control?

I never saw any bus doing a proper unbunch, I guess it only works over some time and if the amount of vehicles is the same over that period.

They do unbunch, but like you say; it happens over time. For instance, if you create a new route, add a single bus, and let LineManager do the rest, the initial addition of buses will potentially appear bunched until the vehicle demand on the line stabilizes. I.e., vehicles will be added as needed, and initially there may be many vehicles added within a relatively short time period to accommodate the demand, the TP2 unbunching will not be able to unbunch at the same rate as vehicles are added.

This is just from my own experience, give it some time to let it settle in. Again, unbunching is not a feature of this mod, that is strictly only done by TP2 itself.