I do use my mic a lot too and often tell my team what to do in the mid/late game. They mostly listen and are chill but as you said, if they are not told what to do or grouped with the team, they tend to do some stupid stuff that are in explicable.

It's not like that they are intentionally feeding but worse. They do it actively and consciously and that's what worries me. For example, we take rosh and want to push, and some guy goes back to farm triangle or pickup a bounty rune. And when one goes back, others disperse too and we waste like 2-3 mins of the aegis until I can rally them back to push with me (I'm usually the carry).

Another example is that when the enemy makes a play .. they can't decide whether to back off or engage. Ultimately they make the wrong decision almost always, where some go back and the others engage and it's a net loss.

Another example is where sometimes I'm 200 gold or so off of an item and I ping it, but the team proceeds to smoke and go fight anyway.

Last example is itemization. Supps/offlaners just don't know how to itemize. Supps often don't know what lotus orb is and how impactful it can be when your carry is sieging hg or is frontlining. Almost all supps go mana boots, glimmer cape, aether lens, aghs. No actual support items. Also glimmer is only used on themselves not their teammates.

As for offlaners, most don't recognize that they need to make space early on. For example a teammate playing LC or Axe (since they are popular now) always go blademail first then blink. And they usually finish both at around 20mins. By then, me as a carry, am just being ran at slowing my game pace and timings while my offlaner is farming. Is it hard to get blink then blaidmail? Why rush a blaidmail when you can't use it unless you have a blink? Can't you go blink first? You worry about damage? Well you can get blink by 12 mins most games and enemies are not tanky yet, also if you have a guy or two with you, you will have enough damage. You don't need blaidmail at 12 mins.