Seeing is believing. Trouble is we wont and haven't seen it all. So you have to rely on 1st hand accounts and stats. I can't credit people who say stats aren't everything. When someone says that they are often attempting to establish the primacy of their opinion over facts. Stats and reports from the day are superior to anyone's opinions. Especially if you haven't seen the player.
The stats have been pretty comparable from every decade since the 20s making comparisons fairly authentic. The batting ave in Barnes' day was transitioning to that trend. In Lohamnn's day the batting average was low however. About 19. Thats gotta tell you something abt the state of the pitches. Which is why, I'm surmising, slow left armers and medium paced right armers dominated then. As pitches improve fast and leg spin bowling come into their own. Which is why I'm not certain Lohamnn, Turner, Ferris etc are transferable to a modern era. But someone like Barnes who could take Hill's off stump after pitching outside leg will always be a champion. Besides the Australian pitches of the time had improved as had our batting. Barnes was the best bowler in our conditions; the hardest in the world at that time.
Even though Barnes' time was one of transition you can still make a comparison with subsequent eras. That is why I think comparing a bowler's ave to the global ave has some merit. The global ave will give clues of the conditions prevailing. The individual ave, in comparsion, how good or bad the bowler is. For someone to establish a difference of 10 btwn his effort compared to the overall ave has done something that people like Marshall have done. And this with only the benefit of a few games against SA. He was special and if anything his ave is inflated due to the preponderance of games he played against Oz.