I had a Juno 6 waaaaaaaaaaaaaaay back, and a Juno 60 just a couple of years ago. Both cool, if limited, synths (prefer the JX-3P for most things but that's a different tale). Loved the arp/punch of the 6/60 (which the 106 I had also didn't have but that instead had a more liquid smooth tone and nice sub end).
So 6 vs 60 over a decade apart I couldn't be used as a witness, but I do recall the 6 was a touch less tame sounding than the 60, the 60 was possibly a bit smoother and maybe cleaner, both punched liked mofos, but the 6 from memory only always felt a bit more raw and unrefined (not always in a good way). 60 didn't last long here as I found it was weak in one or two areas (vs the polysix, JX-3P next to it) and I got bored of all junos quite fast even though they sound beautiful.
As others said, it could be less to do with any designed in differences and just calibration/aging (my Juno 6 I had in the early 90s so was a lot newer than my Juno 60 in 2013 or w/e it was), 20 years newer in fact.