@Andrew Johnson
Your reasoning could be one way to look at it, but not the most common or standard method.
Cap rate is nothing more than another way to value a property. A low cap rate doesn't necessarily mean an under performing property anymore than a high cap rate is indicative of a property with little to no upside.
Remember, cap rate is nothing more than the cash on cash return if the property were to be purchased for all cash.
Asset class (A, B, C, D) and, as you mentioned, location plays an enormous factor here.
In general, the cap rate is primarily indicating the risk of the asset.
It can also be used as a quick guideline when determining which deal to focus on. If you get a number of deals to underwrite you would focus on those with higher cap rates (if buying) first as those are the ones that supposedly offer the best return. Of course that's an oversimplification of what happens as there are an enormous number of factors that also go into whether a 4 cap investment is worth spending time on or not.
To put it another way, the lower the cap rate the less margin of error in both income and expenses you can absorb before the property turns negative. So A class properties with high/stable income tenants who are theoretically less likely to default on their rental payments are considered safer. Therefore A class properties sell for a lower cap rate. The other side of the coin are D class properties with people to live pay check to pay check (and more often than not with government assistance) and are liable to miss their rental payments and require eviction in any given month. That is why D class properties require a high cap rate. They have higher risk, so the return must compensate for that risk.