The difference between the iPhone 7 Plus (188 Grams) and XR (194 Grams) is a matter of 6g. The iPhone 7 Plus is really not that much lesser of weight, unless you’re talking about the (4.7) inch iPhone 7, obviously that’s considerably lighter, because it’s significantly smaller.
IMO anything bigger/heavier than an 8 isn’t acceptable. For my dad anything bigger than a Galaxy S2 isn’t acceptable. Preferably only an SE, like he now uses.