Dave as we know from the other threads that your dabble with Surface products was almost exclusively from a mobile OS perspective to point you was almost unaware of the wealth of software available like MacOS or W10 outside of mobile app stores
Had you been an equal virgin to MacOS as you were to W10 coming from a IOS your perspective and findings would of been similar to the point that MS Office was not in the MAC store (well until very recently)
There is no doubt that IPP fits your needs as you like the few relatively inexpensive yet intuitive drawing apps and only dabble with a few mainstream programmes on occasion
You simply do not require the power of flexibility offered by 2 in 1 like the Surface range and I suspect other than than comfort feeling of just in case, you could almost do away with MacOS too.
I really liked my svelte rMB that my eldest now has and my wife's 2015 1.1 has been trouble free but I put that down to more she runs it exclusively as a W10 via bootcamp.
I'm not sure what to replace her rMB with as she has little requirement for tablets especially as they mainly replicate her phone and she's content with her current arrangement and no excessive duplication that a typical Mobile OS tablet brings
Personally for my very limited freehand skills I perceive no benefit of the IPP marginally or arguably better pen vs all it's other weakness compared to full programmes available on a full OS platforms and not the mainly dumb down IOS equivalents.
I think you should still consider a rMB to compliment your new to be IPP as the portability and so extra usage you gain from this means the rMB is more likely to be used than eg just an IMac or mini sitting in the corner of the room
It was from a mobile prospective but also a computer one, as you will recall i did mention that the Surface Pro 6 is an ok computer. For me MacOS is just miles better in that it's easier to use and it looks a lot better, as i also mentioned lag and freeze ups, something that have never had with my iMac or my 2011 Macbook Pro (before it died). Windows and the Surface Pro is OK in that it's useable, but to me it's not enjoyable, it doesn't have that feeling that the Mac and IOS devices have.
Maybe it's because i'm use to MacOS having used it since 2011. I also pointed out that the Surface Pro 6 was not a good tablet to me it isn't, the iPad is a FAR better tablet. My overall consensus is that the Surface is an OK computer, but it's a BAD tablet! Which got me thinking that because it's a 2in1 device it's trying to be both a tablet and a laptop, in the end i've been left feeling that it's not great at either of those things. Which is a shame!
That's in comparison to an iPad and a Mac, i can't compare it to other Window devices because i don't own any. I think that the iPad is a better tablet because it is a tablet, while the Mac is a better PC/computer because it is a PC/computer rather than watering it down by making either into a 2in1.
I'm really not here to bash Windows, i'm just giving an honest opinion of what i think and experience, there are things that i like about the Surface as well, that kickstand for example is very helpful and the screen is great (retina i believe). Neither to i think Apple is perfect, they have made a lot of mistakes just lately, the price increase on their devices is one, the failure of the earlier keyboards is another. No one is perfect and i think it comes down to personal preference.
I probably could do away with MacOS but i really like it, Mojave is my favourite so far. Saying that tho i do use the Mac for things like Pixelmator Pro, iMove and some games like Two Point Hospital. I like to be able to edit photos on the iPad Pro but also on the Mac when i'm in the home office.
Something for on the go would be a great benefit like the Retina Macbook or the Macbook Air! The Pro would probably be a bit overkill for me. Apple haven't updated the Retina Macbook yet so buying that would be a bad move considering it never got an update last year (which i'm surprised about to be honest).