I get what you're saying, and believe me I do have the highest respect for Snell's achievements, but sometimes fate plays a part in when an athlete is at a peak and who the competition is. Had Snell's career occurred alongside Elliott's and Ryun's, in the same way Coe, Ovett and Cram did, then maybe he wouldn't have had everything his own way! Most of Snell's peers were European, US or from the Commonwealth. There were certainly more nations competing at the highest level 20 years later. Snell's domination from 60 -64, and he did have a couple of shallow seasons amongst those, did not, I believe, prevent other talent from coming through, there just didn't happen to be any other greats in this period. For Coe to achieve at least as much as Snell over both events when the competition was more in depth, is probably more impressive in my opinion. At his best, in 79 and 81, he was as dominant as Snell had been in 62 and 64.
Yes Snell competed in a purely amateur era, but then Coe went into the sport when it was amateur, and it didn't really become professional until 1982, when athletes were allowed trust funds; so Coe was an amateur for at least half his career, and always had a job or was studying throughout his athletic career, apart from 1980.
I do think it's a shame Snell didn't or wasn't able to continue for a few more years, and provide some competition for Ryun, as he was surely capable of much faster times in the longer distance; I'd say around 3:33/3:34 and 3:50/3:51.
I'd also probably rank him #2 all time at 800m above Kipketer, just behind Rudisha, on account of his 2 Olympic titles.