Ron Dennis is not a stupid man. His conclusions may be wrong but he obviously believes what he says, based on facts available to him.
He seems to imply that that big sponsors are only willing to pay up to a certain amount (say $50m) for major signage on a car. Traditionally, the main sponsor provides up to 50% of the entire budget so a team could realistically raise $100m from sponsors with such a title sponsor. However, top teams spend $200m - $250m a year.
Obviously, that is not enough to cover their expenses, especially without large FOM pay outs. Which means the traditional way of sponsorship with a big sponsor and a few smaller ones is no longer sufficient unless the sponsors are willing to pay more for the same space on the car. And with F1 not being very attractive with Bernie at the helm, that’s not an option.
Therefore he is looking at a new model in which several sponsors are willing to share the car livery space amongst themselves for a price which falls between full title sponsorship and the small fee minor sponsors usually pay. With the result being more than a traditional sponsorship setup would rake in.
And in a way, Dennis has been right. There have been very few major new sponsorship deals in F1, certainly at the top teams. ING was pretty much the last IIRC. Martini has gotten a lot of attention but the actual worth of the deal is peanuts.
Sure, there is a certain amount of sour grapes, there would have to be with a dour character like Ron, but he still has a point. If he locks McLaren into a sponsorship for 3 years (usual for large sponsorship deals) at a piddling amount, he faces problems down the road as the team will not have the funds to match the other rich teams. So as long as the team can survive without a big title sponsor, the option to get a long term big sponsor remains. And if the new strategy of several largish sponsors works, so much the better.
Williams obviously wasn’t in that position and needed to sign any sponsor they could in 2014 after Maldonado left to show they were still a viable team after several poor years and a lucky win.