Aye, that's how the alogrithm for laddering seems to work. Kinda unfair, and losing is harshly punished.
Anyway, keep at it, that's the best way. It's a bit like gambling, so be prepared to quit if you're on a losing streak; the gambler's fallacy will make you throw away weeks of hard work as you attempt to right a cosmic wrong. RNG will remain a fickle mistress, and you're going to have to accept that as part of the game.
As for other advice, if you're close breaking 500, you're already well versed with battling, but in any case, have an alt you can use to test teams for any weaknesses before you use the team in the laddering account. Look up youtubers to gain insight on some advanced tactics (wow that sounds real cheesy, my bad), but my point is eventually you'll start playing like a pro subconsciously if you see enough battles where the obvious way out isn't the right way, and you'll understand which Pokemon to sack when without hesitation (something I personally struggle with), and how to lead the battle like chess towards the endgame.
Then again, sumwun prolly has a better idea, he broke 500 in monotype using his flying team iirc so he may be more qualified than yours truly to dish out advice.