iOS 11 needs 4GB of RAM to work properly as it's unoptimised. Various videos have shown Apple losing to even Samsung on ram management in iOS 11. The iPhone X has been hamstrung with lesser ram just like the iPhone 6 Plus was. The current year X will have 4GB ram and function optimally. Gotta keep the upgrades rolling in.
I remember you once mentioned that your 7 plus on 10.3.3 had great RAM management, which was crippled with the iOS 11 update. Back then, I didn't believe you, but after using my old iPhone 5C on iOS 10.3.3, the difference in RAM management was really apparent, and apps stay in memory longer. Now I can relate to what you said back then. Apple definitely changed something about the way iOS handles RAM.
The problem has improved with the 11.3 update, but it still isn't as good as it once was.
I will downgrade my 6S+ to 10.3.3 in a heartbeat if Apple accidentally open their signed window (which they once did) or once a Jailbreak is available. Screw security concerns or battery throttling; I want better RAM management, the old Control Center with toggles that actually turn stuff off, better app opening and closing animations, and no more big ass bold titles within apps!