I think it's up to the individual to choose whether it suits them - it certainly isn't optimal for everyone.
Human's aren't wired to be monogamous (polygamous men and hypergamous women), so you have to resist your natural desires if you are going to practice monogomy successfully, which is easier for some than it is for others.
Whilst I think open marriages can be a healthy thing, it is not without it's drawbacks.
I also don't believe you need to get married to have a successful long-term or life relationship - it is a mutual contract that is somewhat of a barrier, but is much easier to terminate these days (far less social stigma and often there is even an incentive for one party) than it was in yest a year.
The statistics do say that married people live longer and healthier, however they are flawed as they don't measure quality of life, they don't differentiate between happily married vs unhappily married, single and happy vs single and unhappy, frequency of sexual activity, income levels, lifestyle factors etc.The research needs to be conducted at a deeper level.