If you play like a Crystal player, you'll get to Crystal in less than 100 games, guaranteed. It's so easy to rank up in CC. You get free stars from win-streaks, and never lose anything extra. Meanwhile, people in Diamond 5 or 0-credit Crystal are free to throw as many games as they want, without losing anything. (It's a good place to try out new things, since you can't lose ranks, and you get better matches than in Casual queue.) These people should provide free wins to you more often than not. 5 chances that there's one on the enemy team, and only 4 chances on your team.

CC is inflationary, because overall more stars are earned than lost. After the first few weeks, only the absolute worst players (and brand-new ones) will be in Bronze. Then it becomes trivial to climb out of Bronze, no matter how bad you are. You could lose half your games and get Silver by grinding out 10 winstreak bonuses. So Silver will slowly receive those shitty players. Then the same thing happens in Silver. Good players get to Gold first, leaving only shitty players in Silver, and it becomes easy to win in Silver. And so on and so forth. It's impossible to drop ranks, and inevitable that you (and everyone around you) will climb, given enough time. Until eventually Diamond = Bronze, and literally half the population could get Crystal in 150 games or less (1 free win-streak star per 10 games should be easy). This is of course a huge exaggeration, and it would take 100s of games from every player over the course of years to achieve. But the season resets every ~2 months. So by the end of a season it's more like Gold = Bronze, and Diamond = Plat. But the point stands. As time passes, it gets easier to climb. And you can always get 1 big lucky winstreak for 8+ stars to finish the climb. Even if you don't deserve it, you'll get Crystal eventually, assuming you can win half the time in Diamond.

So yeah, sure, if you're the only Diamond 3 player, in a match with 9 Crystals, it'll be a tough match, but you should still win 50/50 against them if you deserve to be in Crystal. And you will eventually climb with free win-streak stars.

Not all Crystal players are good, btw. Anyone at 0 rating isn't much better than a Diamond 1-3, and they might be messing around with jobs they've never played before.