I think you're right. FR's response to this has been to add low frequency routes to all of their new bases. This way they don't outweigh demand with supply. However, an exception to this would be the new EDI BOH route from late September. Two flights a day seems highly optimistic in my mind. Yes, they are trying to compete with flybe on their SOU route here, however, flybe only have 78 seats, and these are hardly ever full.
189 seats is slightly too many, however, that is where EZY and FR will differ now in their business model. EZY are after the Business PAX, with high frequencies, a business product etc etc. FR are primarily after leisure, VFR pax. These pax are more willing to fly at random frequencies (generally speaking).
The only advantage of 189 seats is when they are full in the summer, they will make a killing, maybe not on the fare, but on the extras. You have around 33 extra passengers to make baggage fees, check-in fees, travel insurance, car hire, hotels, on board sales, PB and much much more (dont forget the scratch cards!!)