Simply put, if you give a less skilled player a more powerful starting army, the gap between them and a more skilled player will be greater after 10 battles than after 20 battles.
The Balance template is quite simple in terms of gameplay tactics; there are few opportunities to demonstrate skill, so the initial distribution matters much more than on more complex templates. In other words, there isn't enough time for the less skilled player to make enough mistakes to turn the situation around.
Of course, when the game enters the late stage, you need to perform many actions with different heroes in a limited time – this is where you can show skill, but such situations don't occur as often as fans of these templates claim.