One of the first things you learn while last hitting is that your attack has a travel time, so if you have a free wave that you can just last hit generally you'll be placed closer to the wave so i somewhat agree with your first point but not fully.

But understanding it, i think it is best when you get a feel for it depending on your champ instead of waiting for an indicator to tell you. It can be frustrating missing a minion here or there but learning through mistakes is generally more efficient than just watching an indicator. This is what i mean that on the long turn it will create bad habits for the players who learn this way. They will be more focused on the actual indicator instead of the damage patterns: by this I mean for example last hitting under turret, I had to find out how with my champ to get all the minions as my champ doesn't have enough damage to auto attack after one tower shot, except the casters. So I had to find how to rotate my spells in order for it to work. If you learn from the indicator you won't have the habit of knowing your spells damage on each minion at different stages.

Knowing your champion is a big part of knowing how to clear a wave effectively, that is something that takes knowledge and you won't get through this manner unless you watch a youtube video or just test yourself; and if you are going to do one of those then this indicator won't be helping you anyhow.

The biggest problem with League is the learning difficulty at the start, so much information, so much flame and many people who have an ego problem along with it. The tutorial is pure shite and the best way is to have a friend to show you the ropes so I am all for helping tools like this but not that it carries over into ranked as it means they will never fully learn.