It's not quite as simple as that and may give some the wrong impression as there can be quite a few variations between different ISP's and the particular router hardware being used.
I have mirrored systems with different routers (same data plan) and the contrast is staggering, one particular router combination runs 1.5mb/day and never over 60mb/month, another uses over 300mb month, same system, same upload just different routers.
Well I am sorta going to disagree with you partly but with explanations. I believe it really is that simple as I explained. Hear me out...
First I'd like to premise that I am an IT professional. It is what I do and I won't be going into more specifics and nor going tit for tat with anyone about my qualifications. I don't want to get too technical but I'd like to counter some of your points and perhaps offer some explanations to your observations which I'm not discounting and I do believe you.
To your point that different ISP may give different results. Well that is true. Depending on what their MTU is set for then the same data might consume a different amount of bandwidth, and if your MTU is not configured properly. Congestion, delays and re-transmission (its what TCP does) can also cause bandwidth use to go up. If you are using Jumbo frames or not could affect things too. If you are using IPv6 and it is being tunneled. Etc... And then there is the difference in how ISPs count the data. There are different ways to actually quantify and measure bandwidth. But regardless my point remains that given all these differences and others I didn't mention, it still amounts to nothing. It isn't like you are going to be out of bandwidth quota because you set up a weather station. My point is that most people buy an Alexa or a Smart TV and they don't even consider how much data it is going to use. But for some reason when they find out that a weather station will be constantly uploading data they think that it must use up a lot since it is sending 24/7...and my point is that it doesn't and it isn't any different than any one of those other devices that people never even give a second thought.
To you point of 1.6 MB instead of 300 MB. I do think you were referring to MB and not Mb because they are different and there is no such thing as mb. So I'll go with your comparison of 1.6 MB versus 300 MB with different router but same ISP. I think what may be happening here is that one router is counting download use only and the other router is counting both download and upload use. Just a thought and a possible explanation. But regardless 300 MB a month doesn't break the bandwidth quota if you had one.
Again I want to remind everyone the point of my post was to help those that are less savvy understand that a weather station is no different than any other smart device that people are adding to their homes without even thinking twice. Maybe even less if you consider how much bandwidth a security camera might use and those are getting popular now too.
Your opinions are valid. And I'm only sorta disagreeing, but it is in regard to the message we are sending to new users. So lets look at the big picture. And that was my point to take the fear and stigma out of running a weather station in regards to bandwidth use.