Even in PPSC, a draw is a draw. A country with 1 supply center will receive the same number of vDip points as a country with 100 supply centers (if they have the same starting vDip rating, anyway). The number of supply centers you have only comes into play if the game ends in a solo victory.
The math behind it is a bit complex, but when you are the largest survivor, it approximately boils down to the intuitive answer: You’re splitting the “pot” based on the number of supply centers you have relative to the total. So if you have 1/3 of the supply centers when another player solos, your rating increase will be roughly the same as it would in a 3-way draw. If you “split the map” and end up with a solo victor at 58 centers and the survivor at 57, both players will receive points similar to a two-player draw, though the victor will receive slightly more.
It gets a little more complicated if you are not the largest survivor, because vDip rating change is calculated individually for each one of your opponents. You’ll lose rating to the players who finished with more supply centers than you, including the victor, and you’ll gain rating from the players who finished with fewer supply centers than you, including eliminated players.
It gets even more complicated when you start factoring in the other players’ actual ratings. This is why you will sometimes see low-ranked players gain vDip rating for surviving with a small amount of centers even while higher-ranked players who survived with more supply centers will lose rating from the same game.
However, in your specific scenario, the answer is nearly absolute: as long as the scoring setting is PPSC, you will gain more rating from surviving a solo victory with close to half of the total supply centers than you will from being a part of any draw with more than 2 players.
To give you an estimate of the difference, I plugged the numbers you provided into the rating formula, under the (obviously false) assumption that every player in the game is starting at the same rating. In that case, on the 20-player Modern Europe variant, you could expect to gain 130 points in a 5-way draw or 174 points in a 4-way draw. In the solo scenario, you would gain 417 points for being the victor (with 58 centers) and 410 points for surviving (with 57 centers). Again, these are fake numbers assuming everyone has the same initial rating, but they are directionally correct.
The only reason you would be better off drawing with 3 or more players is if you are an extremely high rated player and the ostensible solo victor is an extremely low rated player – in that case the penalty for “losing” to them would outweigh the larger share of points you would get from your defeated opponents. But the rank difference would have to be astronomical, far greater than the difference between any 2 real players on this site.
This is why some players dislike the PPSC scoring setting, as it encourages the "strong second" strategy - a player with a large number of supply centers is incentivized to help another player achieve a solo victory rather than assist the other countries in forcing a draw.