I already linked you three posts that talked about how this would affect gameplay that you ignored previously here, that would be a good start. Try to address how this change would affect gameplay instead of again focussing on realism.
Some are frontally invulnerable against some things they see, or extremely hard to pen. This patch would increase that number. That is obviously bad for balancing.
It’s a tank at the exact same battlerating, meaning I will see it every match. Even in an uptier not being able to engage someone frontally at all is bad balancing.
We already posted clips in this thread that show situations where that does not help, while shooting the cupola does.
If the Tiger is in a situation where someone has time to aim for his cupola before he clicks on your upper front plate he misplayed. The matchup already heavily favors the Tiger without it losing an important weakspot.