Shapeoko 3 XXL owner here - just going to give my 2 cents…
There is no question that Easel(x-carve) is more mature than Carbide Create/motion (shapeoko). Having said that Carbide3d are constantly updating their software and are really stepping it up to very capable and beginner friendly. I personally use Fusion360 and Vectric aspire to design, these two packages leave both Easel and Carbide Create dead in the water in my opinion.
Mechanically for me the Shapeoko is obviously a beefier machine, having a machine that won’t be outgrown was a big factor for me going with the Shapeoko, I had never seen a CNC machine when I got the Shapeoko and learned it easily enough, I’m still using it today to do small production runs and cutting big aluminium jobs. To me the X-carve is something I’d find the limits of pretty quickly, it just doesn’t have the rigidity I’m after.
Fair point about the forums, the carbide3d forums are still very new and the Shapeoko 3 has been selling for much less time than the X-carve so there are just less people on there, but it is always growing. I have found the people on there very helpful, and have never had to go further than there to get answers to an issue. There is a shapeoko facebook group that is very informative and helpful too. Between those two and this forum I think you’ve got all the help you could need!
I think you can’t really go wrong in your decision between the two, CNC is awesome and people are making amazing things on both machines. It’s just the little differences that will influence your choice, depending on what’s important to you.
Re: the Openbuilds option, the pricing is fairly high considering it is completely DIY, and in my mind the belts aren’t the weak point in the Shapeoko, its the V wheels - I would have put linear bearings on before going to lead screw drives. That’s just me though, it could be a decent machine.