when the right way is so much easier
your first problem is that you think there is a right way.
There isn't one way more righteous than the other, both get the same job done, when strung both get the same sound.
There isn't some MAN who simply decided what is more right. Being a technocrat doesn't give anybody any legitimacy. Therefore both are just as right.
However, I prefer using the thumb.
that's where your second problem lies.
You simply state that index barre chord is easier while knowing that this is not true when you have concrete examples of people who find the thumb version much more comfortable and easier, in addition to Ryan's veritable comment about fill ins.