yeah, know what you mean, but BA get thousands if not 10's of thousands of applications and they've got to filter them somehow.
Alot of this isn't wether you are 'good enough' its wether you fit in the company and I suspect there's also an element of 'are you willing to jump through the hoops' to get in.
Who knows, but bottom line it's their trainset so they set the rules. I'd rather not do essay questions either (I was a maths / science / engineering geek at school and uni - I don't do essays!) but the essay questions ARE there and IMO that means spelling and grammar are essential.