Chinjao was broken, like the filler anime character Naguri (from the Post-Marineford arc filler). As Chinjao himself implied, there are countless conquerors in the Grand Line, but most of them get wasted by the strongest of the flock (e.g.: Roger, emperors, admirals, etc.). Something similar happened to Crocodile (vs. Whitebeard) and Moria (vs. Kaido), despite not being confirmed as conquerors. Rayleigh said that 1 in a million are haoshoku users, so, if we consider that a reasonably precise assertion, the number of conquerors may be much bigger than most of us think.
If we consider that the One Piece's world, for example, has about 180 million people (I'm counting the Arabasta's 10 million population and supposing that the rest of the 170 WG affiliated countries have 1 million people on average each -- I'm not even counting unaffiliated countries like Wano or Elbaf, that seem to be huge), there are at least 180 conquerors in the whole world. If One Piece's population is the same as real life, then there are about 8000 conquerors around the world (I doubt it though, as, according to the latest chapter's revelations, most of the world was flooded in the Void Century).
Considering everything above, Chinjao may even be an above average conqueror, as he managed to survive and even be infamous in the dangerous Rocks/Roger's era. He's just far out of his prime now, in addition of being broken (physically and mentally).