It's not too much of a discussion I don't think. Saris or long tunics don't allow for as much armour and movement when compared to shirts and trousers. Riding a horse wearing a tunic is throwing away your bloodline, and naturally it moved on to favouring standard clothes (now). While being cultural, I don't think the world has lost anything by dressing this way, it's not like in the amount of time lost putting trousers on we'dve found the meaning of life