A lot of the things you mentioned are for balancing purposes, as you said yourself it's an MMO and needs grinding.
We have the Macho Brace which doubles EVs gained, so with how easy EV training is with hordes, you don't need the braces. As for breeding, losing the parents is another mechanic for balancing. If this wasn't in the game you could just breed two perfect Pokémon and pump out unlimited 6x31's which is obviously unhealthy for an MMO.
Most of the things you need to know is either in-game in your Pokedex or here on the forums. Mechanic changes can be found in the changelogs and pretty much everything else in the guide tavern.
Yet another change for balancing. Sweet Scent is used for EV training and shiny hunting, so they put a restriction on how much you're able to abuse it, which makes things such as Leppa Berries valuable.
In gen 6 we had mega evolutions and fairy types, which helped balance the increased Knock Off damage. Here we have neither of those things so updating Knock Off would cause a lot of problems in competitive play.
It prevents you from having a level 100 and just spamming Thief for an easy profit, besides we have the ability Frisk so item farming is already easy enough.
We don't have much post-game content so that's really all there is, grinding.
I tried to answer as much as I could so I hope I helped you realize why these changes were made, I avoided questions like "why is the game harder" because things like that should be obvious considering it's an MMO and they don't want you running through the game without a challenge.