I haven't measured this in any meaningful way but I started using my iPhone Xs Max on Friday, coming from a iPhone X and I use NordVPN with its kill-switch feature enabled. In other words, unless the VPN connection is active it will kill all broadband connectivity on my phone.
This makes it really noticeable to me when my cellular connection drops, as I will notice that the VPN connection drops and re-establishes. Thus far I have noticed that this happens more often on the iPhone Xs Max on my daily commute compared to my iPhone X.
Of course this doesn't have to mean anything. It could be due to congestion at these specific times. It might be due to some additional interference and whatnot. It's impossible to tell but I will keep watching and see if this will be regular thing.
I noticed the same at home. We are doing some renovation so I only have one of our two wireless access points running so WiFi-coverage is somewhat limited. But my iPhone X did not drop WiFi connection when in my bedroom all that often, but my iPhone Xs Max have done so quite a few times so far. Again, this doesn't have to really mean anything but I will keep watching to see if this becomes a regular thing or not.
As cellular/4G/LTE and WiFi+bluetooth are two separate chips, from two different suppliers (Intel for 4G/LTE, and Murata in collaboration with Apple for WiFi+bluetooth) its strange that it would affect both in a noticeable way. Unless the new and improved antenna design is causing some issues? It might also be due to antenna gain optimisation so it can indeed be improved and changed with software and firmware updates.