Sure multihulls are great and I talked here about all the multihulls that are mentioned on that article and much more but they have some big disadvantages:
The first big one is the price: For having an offshore capable multihull able for crossing oceans with a big safety margin you need a big one, like the ones that are mentioned. The same level of seaworthiness can be obtained with a much smaller monohull. Besides size for size a multihull is substantially more expensive.
The second disadvantage are costs of maintenance and marina: Multihulls pay more 50 to 100% on the marinas or on the hard and the cost of hauling out is superior also. Today with the costs of marinas, that's a lot of money.
The third is that a multihull in bad weather is more uncomfortable that a sailing boat of the same size.
The fourth is that a monohul has a better performance upwind. The difference would not be very big regarding a multihull with movable lateral foils but on most cruising cats that's a very big difference, specially if we consider a performance cruiser. The biggest difference regarding a monohull will be downwind sailing, but only if the multihull is a light one and not a Lagoon type that are by far the more abundant and the less expensive. Performance multihulls, like the ones that are referred on that article are much more expensive than the lagoon type.
Regarding comparative performance you can have a look at the ARC:
This year there was lots of cats and you can see they are not doing better than similarly sized monohulls and that's an unfair comparison because price for price you would have a much bigger monohull that would not cost more to you in marina and maintenance costs.
That's true that this year was not properly a normal one in what regards trade winds, that have not been constant, but that's what I am saying: For sailing on the trade winds they are great, for being also a good one upwind, only some very special and expensive ones and even so there are some of those on the transat and the performance has not been great.
Take as example the Gunboat 62 that was beaten by a Marten 49, an Ocean Explorer 60 that was beaten by a X50 and an Oyster 655, a Catana 58 that are been beaten by the X50, by a Grand Soleil 56, a Discovery 55, a Gunfleet 58, a Oyster 48 and a Pogo 12.50. These multihulls are the fastest of the fleet and are fast cats. There are many more behind, some really big ones.
Now, don't take me wrong, if I could afford a 50ft trimaran, or even a 40ft one with retractile amas, not to pay a fortune on the marina and to have a decent interior space, probably I would have one but the only one on the market is an old and relatively slow one (a Dragonfly). The 35 Dragonfly would suit me fine if they upgraded it to 40ft, but the 35ft costs already around 450 000 euros. I wonder how much would cost a 40ft? Maybe 600 000? With that kind of money you can buy a Pogo 50 or any other very fast 50ft monohull and still have money left to enjoy cruising.
In fact most cats you see around are slow cruising cats that are not faster than a performance cruiser of the same size, quite the opposite and even those are a lot more expensive than performance cruisers, size by size. Of course they offer a much bigger interior space, but then we are not talking about performance but about living comfort and interior space.
I'm not sure if you know how to read the race results, but the Gunboat was not beaten by the Marten 49. We took 5th across the line, behind Caro (wicked boat), a Volvo 70, a Southern Wind 72, and a maxi. We beat every monohull smaller, we beat every other cat by a huge margin. I think the performance of a Gunboat is remarkable. We had the most comfortable passage in the fleet with 6 cabins, plenty of privacy. We had a full Thanksgiving, and we didn't motor at all. You have an axe to grind, but you should base your argument on fact, especially when you are using false facts to base your argument. Everyone is entitled to their opinion. In this case yours is wrong.
The rule of thumb (and evidence bears this out) is that a Gunboat is as fast as a similarly sized grand prix monohull (of the same vintage) or as fast as a performance cruiser (of the same vintage) that is 1.5 times the size. And a Gunboat will be FAR more comfortable than either platform. (granted, that last comment is subjective, but...)