A high AC front liner is not necessarily high strength. High Dex can also come to play. An elven eldritch knight can reach high AC and not be trained in athletics.Well, of course, but that is pretty realistic isn't it? To have a game where having extra numbers in battle isn't a contributing factor is pretty poor design. I agree for many tables advantage is too strong, so my idea offers a method where numbers can still matter, but not as much as normal flanking would.
Anyway, also with my idea you would need a large number of allies to come close to giving you the same increase advantage does. Given the numbers above, of a 6-4 battle, if things happen to get "spread out" more evenly (2-1, 2-1, 1-1, 1-1) then two ogres would get a +1 and that's it. Not as big a deal, is it?
The big deal with your method, is that flanking bonus with advantage becomes much more powerful than normal. Again, 4 ogres against a PC will get a +3 bonus. Now, if the PC has a high enough AC so that the ogres have trouble to hit; they will try something. So two of them will help the other two. In normal circumstances it means that they simply have advantage and their normal bonuses to hit. If the character actively dodge, then only get their normal bonuses to hit.
With your method, they will have +3 to hit (as the helping ogres are still a threat so warrant the flanking bonuses) and will have advantage and their normal bonuses to attack. If the character dodges, then they are still with a +3 to hit in addition to their normal bonuses. That is a lot.
And the higher the players are, the more dangerous and unbalanced your approach becomes for one PC.
Imagine trolls, giants, glabrezu, Four of these can surround a PC in no time in an open space.
What about a few gladiators where a cleric is blessing them? Or even worse, high level thieves or assassins? The more varied the monsters, the more swingy a battle can become. 5ed removed the +"x" without concentration approach for a good reason. 3ed was a nightmare in bonuses calculation and with so many different spells to boost both sides...
But maybe it's just me. What I know is that since I have removed flanking, players are now reaching much higher levels and TPK are much rarer (but still present).