Apple knew the X would be a stretch for some in terms of cost and changes, so they released the iPhone 8 and 8 Plus at the same time. Mainstream fans who are ready to upgrade (mostly users of the iPhone 6 and older) have a safe and less expensive option in the 8 series. My mother just upgraded from a 6+ to the 8+ and she loves it. The reason she loves it? She said it's exactly the same as her 6+ (meaning there was no learning curve), but it takes much better photos of her puppers.
I don't think true mainstream users think as much as some people do about switching between iPhone and Android. Most mainstream users avoid change and nothing about the iPhone 8 would drive them to Android. Mainstream users don't complain that the 8 is boring because it's just like the 7 or the 6. The fact that it looks and feels like a faster/better version of the same iPhone is a virtue for them. If you like to switch platforms or upgrade to a new design like the X because you enjoy the novelty, or because you obsess over the display, or because you obsess over the hardware and performance specs: You are not mainstream.
If the X did not exist, and the iPhone 8 was offered as the only flagship, would you have stayed with Apple instead of switching to Samsung? It sounds like you were just ready for something new, and the Samsung appealed to you more.
That means you are not mainstream. I have a lot of mainstream smartphone users in my family and extended family. Most are iPhone users and a few are Android users (it's very clear who is who because of the whole blue bubble vs green bubble thing). When I say these are mainstream users I mean they don't even know when a new model gets released. They don't follow the hype and watch announcements from Apple and Samsung. They don't get as excited about new features or improvements. They only get interested in upgrading when their current phone starts to feel slow and/or has trouble holding a charge throughout the day. They actually kind of dread upgrading, because they don't want to learn anything new, but they do look forward to getting a new model that simply works better and faster. They don't care if it's the best and the fastest. Just better and faster than their old device.