The people who hate Flash are obviously not the ones who use Flash, and the ones who use Flash know that there is still no replacement that comes close.
The thing with Flash is that 10 years ago, it was awesome. All browser games and animations ran on Flash and it was super easy to code and create, so even 15 year-old me could make a game with zero knowledge about animation or coding, and still make something that plays like a real game. You can't say the same about coding games for iOS. My PC from 1999 could run Flash just fine 10 years ago, so performance wasn't an issue at all.
It became an issue when things shifted from desktop PCs to notebooks and especially phones and tablets. Things had to change, but the price of that change was that people had to learn to code properly and more efficiently, and Flash was never designed for that. That's great for people who can code and who make money off this. But for people who just played around with coding, it meant that they had two options: either learn to code properly or give up making games altogether. Either turn your hobby into a profession or give it up.
This meant that such games now often cost money, which was unheard of when all games were Flash-based. If you make something for the App Store, you put a lot of effort into it so you want to make money one way or the other, at least to pay for your developer account's yearly fee. You can't really just fire up your iPad and play 20 random games for free in a row. You can, however, take your computer, go on Newgrounds and play thousands upon thousands of Flash games non-stop for the rest of your life. Try doing that with iOS.
When my 7 year old nephew comes over, I just put on Newgrounds and let him play whatever he wants. He can't believe how many games there are to play, as he has a tablet at home which requires you to find and install every single damn game, and the good ones aren't free, and most are "trial" or "freemium" versions and crappy games that would work much better with a keyboard.
Tablets are meant to be the ultimate casual gaming device, but they simply can't beat my crap PC from 1999 that runs Windows XP despite having way more processing power and RAM. I find that a bit odd.
HTML5 is a perfect replacement for simple Flash animations like ads, but there is the world of pretty good (better than the average iOS game) free Flash games that is simply not being replaced by any new technology so far. And even if there is a way to do that, it will certainly not be something very easy to learn for someone who isn't committed to doing this professionally. If a kid wants to learn how to make a game but has the attention span of a goldfish, you may just get him to learn something with Flash as it will only take 10 minutes to make a simple game, but try teaching him XCode and you won't get very far, not to mention you won't even be able to play the game on the device without paying for a developer account. And what else can you do?
To me Flash was a way for someone who has no idea how to code to get into that wonderful feeling of making a game and playing it, sending it to their friends without them having to download anything, with a minimum amount of effort and knowledge. I don't think that when you make your first ever game, you really care about the performance and the sound of your PC fan, you're too busy enjoying what you created.
Hating Flash is like hating records because they're too big to fit into an iPod. The world evolves but that doesn't mean the old stuff is inherently bad, it's just that the new stuff has different priorities. Just like records, Flash has some nice things about it that work for those who like it, but no one expects it to be in modern consumer devices. That's not a reason to say it sucks. Just like records, if it's not your thing, don't use them and you'll be fine.