what's the difference between 600-700-800?

Frequency of blunders, general theory knowledge in chess, opening prep depth. Varies from player to player, but on average it holds that at each rating band they play slightly better than the preceeding one. But if you get your chess habits together for consistent play you may notice less as they become beatable. I went on a rating drop to the 600s in blitz when playing bad chess habits and struggled to get back to 700, but when I improved my playing and thinking habits for chess I rocketed past 800 into 900. I still play bad chess at times, but what I know from study comes easier. Lower Elo players probably know much of what they need to be higher Elo, they just have bad habits and it comes together every so often for good games. So, all that to say yes play as a group reflects strength of past form, but you get outliers that over and underperform game to game. Just work on your habits.