Anyone who concludes that Test cricket is the only way to rate players and that the domestic First-Class game has little to no part to play - and that this is the case for all players throughout history - doesn't understand how the game has worked down the ages. There were times - and it isn't anywhere near so long ago as you might think - when some of the better First-Class cricket was superior to not a little Test cricket.
Just because for the last ~20 years Test cricket has been the obvious and ultimate format of the game - and a player (exceptionally rare though these cases are) who succeeded at Test level and didn't do anywhere near so well at domestic FC level can have that near enough discounted - doesn't mean it's always been the way.
Even in the 1960s and 1970s, some of the better domestic cricket was of a higher standard than Tests. Of course for any player until those of very recently, domestic FC cricket has a huge part to play in an assessment of how good or otherwise a player is - regardless of whether the player has had a decent shot at a Test career or not. To suggest otherwise is IMO foolhardy.