It'll be interesting to see which type you think seems a closer fit. Seems like a lot of ISTPs initially identify as INTPs.
I could have pretty much written your OP verbatim.
What narrowed it down for me was the proposed exercise, which I like in thinking it follows the Keep IT Simple Stupid principle.
The other element was noticing my impatience with NT free flow when considering possibilities vs. focusing on a more immediate and practicle solution.
Plus an observation that it's a lot easier for me to pick-up and eventually master skills in the physical world vs. ?
i.e. First time I ever got on a dirt bike. I had no trouble making my first round of the track, taking it through the woods faster than my more experienced companion and jumping it like someone with more experience.
A couple of funny things happened, when a couple of NT's tried... They either couldn't get the bike going, or it flew right out from under them. I won't say that'd universally be the case, but it's a differing kind of focus of natural attention.