1. Group stealth which the current rules makes nearly impossible (4-6 rolls means a really high margin of failure, even if you have high modifiers) is a feature and not a bug, because Ranger spells.
Uh....no...That's not an acceptable answer. lets say each individual character has a 20% chance of failure on the dice (meaning they have extremely high modifiers). Lets say we have the average of 5 characters. This means the chance of one member of the party failing is 1 - (.8 * .8 * .8 * .8 * .8) (multiply together the chances of succeeding at a roll to get the chance of not making it) or 67.232%. So if the entire party has an 80% of success individually, they have a 67.232% chance of being detected anyway as a group. I'm sorry, but it appears the team at WotC didn't run the math, or they have a desire to make the group reliant on magic. Just for fun a party that has members that have 20%, 20%, 20%, 40%, 60% chance of failure would give us 1-(.8 * .8 * .8 *.6 *.4) = 87.712% chance of failure. So if you have even one member that has a low chance you might as well not even try.
2. There are features of medium armor that make it worthwhile.
Sure, especially that near 100% chance of failure of group stealth checks from above. If you have disadvantage on stealth checks that means your party is probably going to fall into that 87% or more chance of failure so no one should take heavy armor, unless you have a Ranger with the right spell, in which case everyone should take heavy armor.
3. Yes, the changes in bonus actions are meant to completely nerf the usefulness of rogues two weapon fighting, we just can't tell you straight up.
What did you think would happen? Someone pointed out a broken combination and they nerfed the system to accommodate it. So now it has the trickle down effect of nerfing everything it comes into contact with. This is what happens when you don't test everything (that is every combination of features, feats, and spells that can come up in the game) that you design. Were you expecting anything less?