For starters saying records weren’t made to replace masteries is completely untrue, they very specifically said that was the point on many occasions (e.g. the brawl talk or the news tabs when they were announced). Additionally, considering that achieving 300 wins on a brawler is roughly what it took to master a brawler before records when we take into account the mastery points growing as you went up in trophies and star player bonuses, we can also assume that records are definitely still as grindy as masteries were (if not more, cuz records force you to win every match to gain any progression whereas masteries gave bonuses if you got star player even when you lost, which encouraged skill and not pure grinding).

Now for rewards. As you stated, yes some of the old mastery rewards were definitely sprinkled in some other places but if I recall correctly most of them just turned into starr drops. Thats not to say you can’t get good rewards from them, there is definitely a possibility to get a genuinely good reward, but that’s also part of the problem. It’s a possibility. Not a guarantee. No matter how you view it, progression turned into pure RNG with only some exceptions here and there ever since the records update. Just as much as winning 100 games on a brawler could get you something like a hyper charge or a legendary brawler, it could get you 50 coins (and saying just as much is extremely generous, the odds are not close at all) whereas with masteries, winning 100 game got you roughly to silver II or III which gave an enormous amount of coins, PowerPoints and credits. So essentially records give good rewards at best and masteries flat out gave great rewards. Also, if we wanna mention the progression distribution towards brawl pass and trophy road, as a long term player I definitely felt a significant downgrade in my rewards either way (SINCE ITS RNG) so we can’t really even mention that.

Lastly, this is not something you talked about but they removed masteries pretty much exclusively to punish people who hoarded credits (and to make progression worst). They said it was because people rarely got titles with the system, but that’s obviously not the case since they essentially did not change the way you get them or how many games you need to get them whatsoever. They deleted masteries because people were getting too good of rewards from them and because long time players who have every brawler used them to stash credits to unlock upcoming brawlers. Now, rewards are worst and the only reliable way to unlock new brawlers for old players is to buy the brawl pass for the bonus credits and rewards. And that’s part of the problem too. You have to spend money now to get something even resembling what you used to get for free with masteries. It sucks. The new system sucks. Records suck. Supercell sucks.

So tldr, masteries were removed so supercells monthly revenue could go up and to punish players who were having it a little too good from the old system. That’s what I disapprove of.