You're coming from iPhone 6, which was Apple's thinnest phone ever at 6.9 mm. Any new iPhone will feel thick due to the larger camera sensor and glass back.
It's like the iPhone SE people calling the XR big. For 2018, it's not a big phone at all.
Compared to current offerings sure, but not to legacy phones. Look at the new IPP, thinner and less weight than my current 12.9 which is why I'm upgrading. Back to the phones, larger, heavier, umm no. I'm down for a 5" to 5.5" X/Xs type device. Light weight is important to me and so are dimensions. I carry other things on my person. The Xr is a phablet. Handled one in store. I use a case, always, so it's too large. The Xs has cellular connectivity issues and it's also my absolute limit in size/weight so assed out this year. I'm fine with that as I don't upgrade devices annually. PC every 4-5 years, iPad, every 3 or so, phone I'm used to upgrading every 2 years until now. I'm content with that but even with a brand new battery, the current iOS is eating up my battery faster (iphone 7) than any iOS before it. Hoping for a smaller option in 2019. I see usb-c and 5G LTE on the horizon anyhow. Via my carrier, and selling my current device, I could just about get a Xr 128gb for almost nothing or a Xs for $350 but the Xr is too damn big and the Xs has connectivity issues I won't deal with as well as the chance of PWM/eye issues. I think they should have made the Xr 5.5" or less and charged $49-99 less for starting price. 6/7/8 users and SE users got the back of d's in 2018.
But this year, and last, has seen a change in Apple's prices for most everything. Some substantial increases on phones, iPads, and computers such as MM and MBA. For me it will backfire on them. Like many, I'll be holding onto these things much longer now. Continue with it I'll start looking elsewhere which is a shame as I'm fond of the eco and integration but for me this pricing model won't hold. It's getting silly to me when I can get a state of the art 4k HDR Sony flatscreen for less than I can buy a phone or iPad. Apple is pushing pricing to the extreme and at the same limiting the offerings or cutting people off that want a smaller form factor device.