There is a built in bias for going with what you know. People that know the current crop of players, but never saw Mosconi play, will tend to be biased to believe that somebody (or more) from today is better than Mosconi. It is the reason that often times people feel the pro that lives in their area who they have been exposed to the most is the best (Larry Nevel fans as one example, but around Atlanta they tend to think it is Archer, etc, etc). It is the reason why a cue maker's cues are far more popular around where that cue maker lives. Aside from availability, a disproportionate number of local people actually feel that that cue maker makes the best cues available anywhere.
On the flip side though, people are also biased to that which they experienced in their youth. For whatever reason it is human nature to feel that things from their youth (teens and 20's usually but could be any time in the first half or two thirds or so of your life for those that are "older") were better than they are now. You know, the "back in the day" thing. People tend to think everything was better back in the day, the music, the tools, the machinery, the cars, the pool players, etc. People that are in their younger years today will be saying 46 years from now in the year 2060 that Shane Van Boening was the best of all time even if there are several new players in the year 2060 that are twice as good.
The fact is that both sides are equally biased and one side can't use the other side's bias as an argument against them when their side has a bias just as big. What makes sense is to look at everything else where there is objective rather than subjective measurements to see if people are better at it now than they were 60 years ago. Take any other sport or endeavor, and I mean any (even the ones were equipment has no bearing), and people are better at it today than they were 60 years ago 99.9+% of the time (at the top and in depth of field both). Logic tells us that pool players aren't an exception and it holds true here as well, regardless of what our subjective opinion tainted by bias might tell us.
On a side note, another thing I often see that skews people's opinion about someone is how much they dominated in their time. This obviously has zero to do with their skill level (only their skill level as compared to everyone else's at the time), but when someone really dominated an era in something, people's opinions about that person's actual skill level often get irrationally elevated. Using Mosconi as an example, he absolutely dominated during his time which was also for an extended period of time. Nobody today has even come close to that kind of domination. As a result, many people will tend to attribute more skill to Mosconi than he really had. Even if the top 50 players of today all had more skill, some would never be able to see it because none of them are dominating like Mosconi did and that has skewed/biased their opinion of Mosconi's skill. Skill and how much you dominated are completely separate when comparing eras but not everybody can keep them separate on a subconscious level.
