I was asking the same question a few months ago (you linked my thread in your post) so ill try to give some advice from the same position.
Firstly id ask you which one is more valuable to you. Performance vs Form. If you literally cant do what you want to do (or do it efficiently) without the power of the 13 then the 12 is 100% out of the question immediately. It seems like you are preferring the 12 so if the performance of either is fine then thats the one id get.
Another option, since it sounds like you really want the 12 if it only had more power, would be to reuse your old laptop. You could just keep the old powerful one plugged in to an external monitor, power, and keyboard all the time and use it when home, then just have the 12 when you want to draw. If you needed the extra power outside then you could just remote into the old one.
I still have my 13 and havent gotten a 12 yet. Im mostly just waiting for the cracking issue to get absolutely fixed (from what i understand, they fixed the bottom but not the top and are still sometimes accidentally shipping out old bottom covers) before i switch. Im also not sure whether single channel ram on the 12 is fine anymore with the ram shortage and dont really want to give up my 48gb. I still plan on switching since i also like the form of the 12 and dont need the performance that much, but at this point i might just wait for a performance upgrade since it probably wont be too long until we get one (dont listen to me i have no clue).
Hope this helped!