FWIW Dept.: As an ex-XPRO2 user, XPRO-2 is a good camera capable of excellent shots. Lots of people love Fuji colors and JPEG's (Acros sim). Fuji fans scream about Fuji's firmware upgrades, but frankly neither of these are as unique as the buzz. There are many who find Fuji colors not to their liking, too, or difficult to manage. And as Leica fans will note, the hybrid viewfinder is definitely NOT a rangefinder, and even most X-PRO users will rely on the EVF most of the time according to polls on the Fuji forum. Fuji seems to be of several minds on how to use these cameras, and there is something in this that results in a mix of handling matters that either fit you requirements, and meld with what and how you want to use it or not. I'm a fan of rent-to-buy as a trial, and lensrentals.com has a decent program for purchasing keepers as well. I can attest that if you do buy and you buy with the service contract they offer, the service is both first rate and speedy: one-week door-to-door in my case.
That said, I'd argue that if you like the rangefinder style, the Leica's whole style is designed on this basis, and the handling issues likely more consistent with the approach for which it is optimized. Fuji will open the box and allow you to use your camera for a wider variety of things... more readily, but again, at a cost in terms of fitting the dedicated form and shooting style. It's close, but not going to be the same. And if you're considering a Monochrom M, you're pretty far down the path to favoring a definite shooting style that I would think the Leica will fit more readily. Note that I don't have a Leica.
FWIW, I believe shooting begins with lenses - the sharpest and best handling you care to buy, and then looking for an optimized body to shoot them on. Shooting on the native body is best, but you can usually run them more widely - but there is a cost. And you can adapt your shooting within a range of workflow, but it takes some time to get comfortable. If you want full frame, and if you're printing, and I think full frame adds more than an academic difference in this, the Fuji's APS-C may not fill the bill. It's good, but there are other options; and without IBIS, it's not as good at adapted lenses as some alternatives (e.g. Sony A7 series).
All in, there's a difference between a B&W raw image and a B&W jpeg, and it is NOT academic. Leica is also one of the few I believe that runs the histogram on the RAW image rather than JPEG. Ditto - not academic. If you want to really find your shooting channeled into an optimized fashion for B&W, you're going to drive down toward the M Monochrom... even the 18MP version. Fuji will not do this for you. I'm thinking of this hard myself, but also like the M10. It's a question of $'s, and I have to ebay some old model trains first to justify the re-allocation of time, space and $.
End of the day, I think the question is more one of whether you see this as a keeper camera or whether it would be a "phase" or "stepping stone". Any one of these can justify the decision in my view. By today's standard, it's merely tuition and cheap at the price if you'll commit to it and use it. In some measure, ANY camera can be constrained to teach you certain things you want to learn, but if you want to be restricted so that you HAVE to do it, then by all means a Monochrom (or maybe even a B&W film M) seems an excellent bet. Worth every penny, and from my perspective, the lenses are waaaaaay better than Fuji by design... as their form follows their function. With Fuji... form is whatever they want it to be... and focus by wire is a toss-up decision rather than true-to-purpose given.