The Edo rating is so broken that the author had to go in and manually adjust some of the more ridiculous results. But both Edo and Sonas start with the premise that a player who was acclaimed as a master must be at least 2200 strength, and a world champion must be at least 2700 strength.
One problem with ChessMetrics is data bias. Sonas used a played-games database. Because many, if not most, games played before records were adequately records, the retro-ratings are skewed toward the winners of published games.
On the otherhand, Elo used wins, losses, and draws from tournament and match tables (more likely to be to be saved); the indivdual game moves were not necessary.
Old GM would probably play poker or Russian roulette these days. Current chess would lack the aesthetics, adrenaline and guts they sought back then over the board.