Leigh: a 60mp back will easily produce more on-print detail than your 6x6 Agfa 25. Comparing final-print detail compared to a very well exposed, carefully scanned, perfectly focused fine-grain 8x10 inch piece of film is still a relevant debate. But resolution vs 6x6 film was settled long ago. That's not to say that [Film vs Digital] is settled - they are tools, and as such have different pros/cons; neither is "better" overall, just very different. BUT the resolution thing is empirical and easily demonstrated. If you'd ever like to try a digital back to see this for yourself we'd be glad to help; I VASTLY prefer to have someone do this test themselves then to talk back and forth about numbers or use previous tests, but here is a 32mm HR lens with an IQ160 (60mp back) for you to download and print as big as you want and compare to any large prints you did back in the day on Agfa 25:
28mm & 32mm Lens Comparison - DT Blog
Regarding Hassy lenses: they were best-in-class, but their class was [lenses designed for film]. You'll find they still draw beautiful images, and still focus with wonderful manual mechanics (as compared to say the Canon 85/1.2 which is on a delayed fly-by-wire focus system even when manually focusing). And for several of the lenses, like the 120 Macro, that the resolution is excellent even for 60mp or 80mp.
But you will find, compared to modern lenses, that they have more chromatic aberration, lack bite (which you may like or dislike depending on your aesthetic) and that the wide angles don't hold up at the edges for work like landscape where edge-sharpness is traditionally considered important.
If you compare the Hassy SLR wide-angle options to other modern medium format wide angle options you'll usually lose, but not by so much that it couldn't be justified based on the very low cost of entry. If you get the Hassy pancake body with the 38 Biogon you'll likely be very pleased relative to most modern SLR wides.
BUT you know at the end of the day what you want is a tech camera
. Those wide angles will beat anything you've ever seen.