Too small, slide mounts were already standardized on 24x36, and the square was never all that popular among the general photographer. The reason why the square shape in 120 was originally developed was a technical hack. Since it outputs a square, there was never any need to hold a Hasselblad vertically; just take the photo and crop it to suit. The only square consumer oriented cameras I can think of are twin-lens reflex cameras like the Rolleiflex, which are delightful but somewhat uncommon. A number of folks started trying to make use of the square format as a square format, but it was not originally, I think, intended for that purpose.
Re: too small; an 8x10, one of the smaller standard print formats for portraits, is about an 8x enlargement from a 35mm frame. With modern materials and good technique, 8x-11x is feasible, but starting to push it at the edges; I have printed 13x17s off 35mm but I would not want to push it much larger. 35mm does 4x6s, 5x7s and 8x10s perfectly reasonably, which is what it spent most of its time doing for common consumer work. It's worth noting that one of the other common consumer cameras of the 1940s was the Brownie, which output 6cmx9cm images and was routinely contact printed, producing something smaller even than a 4x6.
120 produces images that are between 1.8x (in the 645 format) or 2.5x (in most others) as large, physically, meaning that the common enlargements are only 4x-5x. If you push it, with quality equipment, you start getting into print sizes that are super clumsy to handle like 20x24. I've never printed, personally, anything larger than a 16x20. If you do your own wet processing they're also nicer to work with—35mm negatives are real small and kinda fiddly. 4x5 sheets are also delightful to work with, of course, but they require fighting the camera in the field.