You are probably a lot harder to replace and a lot more skilled than many of those several hundred "core" employees. You probably are a "core" employee, it's just really convenient for them to not think of you as such.
As long as you don't complain or jump ship, they'll just keep doing that. Of course it's not all that tempting to jump ship, since even businesses that are "inherently software business" underpay developers, so if you're comfortable where you it's hardly worth it to move on for a few extra bucks. Despite the fact that all of those businesses are definitely whining loudly about the scarcity of developers.
Hell, even if you are "peripheral", if the same company needs to invest huge sums of money in office space, equipment or other "peripheral" stuff to "support" those "core employees", they will simply do the math and pull their wallets. It has nothing to do with "peripheral", it should be about scarcity and economic value. Paying you twice as much won't make a dent in their spreadsheets, nor will it make you insanely overpaid compared to many other employees.
But unfortunately in reality nobody bothers to do the math, it's all about "perceived" value, and as long as both you and your employer live inside the reality distortion field that totally undervalues developers, you'll continue to get underpaid.
The few companies that forget about prejudices towards techies and simply do the same cold hard math they apply to every other investment have absolutely no problem paying way above "market rate".