This answer is about hero buffs and 2 teams SD.
I am pretty sure that waiting in base 40 minutes is not something that is happening often, its mostly a unique case scenario. If at 20 mins all other teams left or got destroyed, the game offers many counter tactics to fight turtle/camping players. (Nukes, medivac, siege tanks and more). Unless if the player that is camping is way behind (more than 5k) so he cannot fight back the enemy units and camps.
In that case, a good hero play can still earn some feed, before SD occurs (25+ minutes time)
(I am talking about public games)
About 10 min SD if 2 teams left, i see that is just not possible in 10 minutes to turn a difference bigger than 4k, (I am not talking about a pro player against a new one, while even a pro player might have issues if there's camping). Allow me to use something you said: "When a team is getting the lead out of new players early game, having 60 min SD gives you the required time to fight back and turn the game." Yes, having 1 team to feed, doesn't mean its not possible with good hero play and using counter tactics to turn the game or earn some good feed and catch up while having more than 20 minutes time till SD.
But having a 10 min SD when 2 teams, will not be good in case a team got fed a lot early game and both enemy teams left during 15-20. These 10 minutes simply will not be enough and the best option will be to quit and start over.
We don't want to change MA in a way that is impossible to do anything to fight back, that's the reason the game has all these counter tactics, and we looking to add more.
Hero buff in order to comeback or turn the game in just 10 minutes...again i say, nothing is stopping a player from taking these buffed heroes and use them early game. MA had an OP HT before, same for Infestor being very OP able to snowball in just 10 minutes time, and in about 20 mins, the infestor player had a lot of feed out of pubs.
Like i wrote in an earlier post, many times during public games an experienced player is playing against players which some might have experience and others might have zero.
So in order to keep proper balance, we must be very careful about the buffs that take place on a hero. Current heroes if used good they can still earn a lot of feed out of pubs, just without snowballing very big and making the difference impossible to catch up even for a good player.
But we know that even now, snowball does exists under certain scenarios, and this is what we want to remove as much as possible.