Once the playoffs start, it's essentially random; whomever can play well enough to win three playoff series wins it. A team may feel better about their chances because they had the better record, but it doesn't seem to help them win more in the postseason.
What? Random?
While there is no law of the universe that says you have to have a strong, winning team with league best hitting and/or pitching and/or coaching, I would never use the term random. Why aren't the Twins in the WS? Is that random? How about a team that has a record of 90 wins vs. a team with 95 or 99 wins? I would tend to go with the team with 99 wins over the one with 90 over a long period of time, season after season.
A hundred years from now, assuming baseball is still here, which I hope it will be, you will see a curve develop where teams with better regular season records tend to do better, or have a better chance at or in the postseason. If you have a terrible season, and lose more than you win, you just won't go to the postseason. Winning percentage is just one indicator, but not a good one to overlook.
But when you say random, it's more appropriate to flipping coins:
Let's take an example of flipping a coin.
With one toss, one side will come up and the other one won't so one side will be given a value of 100 and the other a 0.
Let's say you toss again and it comes up the same side (let's call it heads), heads still retains coming up 100 percent while tails comes up zero percent.
Flip the coin six times. With that, chances are you won't get one side six times but it can happen.
Flip the coin six hundred times, then it's less likely to come up all heads or all tails.
Flip the coin six million times, and then it becomes highly improbable, though not impossible, to come up on one side every time.
But stretch that number out to infinity, and then you will have a value of 50 for heads and a value of 50 for tails. It won't even be 51-49, or 49-51, rounded out, over the course near infinity. At infinity, it will be literally 50-50.
Certain things have happened in baseball, and will continue to happen season after season, but over the very long haul, let's say 200 years of the sport, and more so in 300 years in the sport, the WS winner will more likely be the one with the better record and/or pitching and/or hitting and/or coaching, or a combination of those attributes.
But:
That being said, I hope the team that's in the WS who had the lesser record wins this one.

It's the fifth and it's 1-1. Hang in there, Philly! Though I tend to go with numbers, I hope that both teams are essentially, randomly equal (which they aren't) and Philly comes up heads.