So Hansa small countries will need ridiculous bonuses to have their strengths properly represented, nice.
It was much more about landlocked OPM like Aachen or Ulm, than Hansa. First can forget about been significant traders if they not expand, but later has a very strong position even with relative small size.
Firstly, although it is better to control as much provinces as possible in important for one trade region, some provinces generate much more trade power than other.
So at the start of demo Hansa provinces generate from 10 to 20 tp, when almost all other provinces have 2 or 3 tp. There is only one arbitrary modifier, which gives +5 flat bonus to trade power. There are near 50 provinces, that have it, including 2 Hansa's. Also Bremen and Hamburg have + 10 tp for being placed in river estuary.
So despite being 3PM Hansa have trade power equal to country, that has 10-15 standard provinces. And there are only two important places in Lubeck trade node, that did not belong to Hansa. It is Danish capital, which has Sound Toll modifier, and capital of Pomerania which placed in Oder estuary.
Secondly, Hansa has a very large naval limit and starting fleet equal to Denmark one, which give significant boost to trade power.
Only problem with it, that now moders can't divide Hansa on proper three independent cities, without nerfing their capabilities. But maybe Paradox return to trade leagues mechanic somewhere in the future. Or modders will find how to implement it.