That's an issue with the entire Marvel universe, not just the X-Men mutant side of things. Wakanda canonically had the cure for cancer for ages and IIRC still hasn't shared it with the rest of the world. Tony Stark had Extremis perfected enough to distribute it as a subscription service app on people's phones, and that stuff can reprogram the body genetically and cure anything permanently if you want it to. Multiple sets of heroes have access to advanced alien technology. And of course it's not just medical stuff, it's the same for clean energy (don't forget, Tony had Shi'ar contractors build a partial Dyson sphere close to the sun to power a massive weapon in Time Runs Out... wonder if he still owes them on that contract in the new post-Secret Wars cosmos), agriculture, transport, everything.
Not to mention the Osborn-led iteration of Hammer/HYDRA cracking the code for duplicating any superhuman's powers, including those that come from the X-gene like Wolverine's healing factor, way back in Bendis' run in the Avengers books, and broad spectrum power nullifiers being introduced in the same storylines - how is Orchis not stealing the nullifier tech, and the U-Men not switching over from gross body part transplants to gene therapy ala those storylines?