You're confusing things in your post.
Suburbs are not always separate things from major metros. Often times, suburbs are a part of major metros. Being in a suburb in a major metro isn't as good in most cases as being in the principal city of that major metro. The experience in the suburb will be worse and you'll perceive the major metro as shiit simply because you chose to live in the wrong neighborhood. If there are suburban environments without a major city nearby (these are often smaller cities of around 50-150k), that's a different experience.
A lot of one's success in dating in an area comes down to their social network. I've seen guys in metro areas of 300,000 have an easier time with dating than guys in metro areas of 5 million + simply due to having a stronger social network.
Smaller areas (less than 150k population) tend to suffer from a lack of choices. If you're some guy who finds himself single after the age of 25 and you're in a smaller area, you likely need to move to a bigger area if you are able to do that.
The middle sized metros (150-600/700k) are often the best bet for dating. They are big enough that you'll have some choice but small enough that you won't run into the problems of the major metros. In the smaller areas, the lack of choice is killer. In the areas with 1 million + metro population, the competition is fierce and the women are ultra demanding.