Obviously it depends on where you are coming from. We live near Guildford and Portsmouth is a lot quicker to reach than Southampton so the Fishbourne route is a no brainer. (Lymington is out of the picture altogether).
I quite agree that the loss of the half hourly savings represents a deterioration in customer service (We are in fact booked on the 10:30 from Gunwharf tomorrow.) but it isn't about customers, its about money. Bigger ships can carry more with only a marginal increase in crew numbers per vessel. They are proportionately more economical plus less sailings are needed so big savings there too. From an accountant's view, what's not to like?
I doubt if traffic will suffer unduly because holidaymakers can readily accommodate hourly sailings if they only visit occasionally and book well in advance. The commuters and business passengers probably have no real alternative option in most cases so will simply have to put up with what they are given. I imagine any traffic downturn costs in this sector will be covered by the savings.
From the customer viewpoint I always felt that the four Saints worked very well, offering a frequent service on ships designed for the route and offering service operational flexibility plus resilience if one of the vessels was out of service. St Clare is literally a 'white elephant' and doesn't fit the route requirements so well. If one of the two 'biggies' breaks down then there will inevitably be severe problems.