As an anecdote I would have never expected, English Breakfast tea standards are the poorest: broken leaves that fall apart while producing finer sorts.
I think English Breakfast tea leaves are deliberately broken when processing as it gives it a stronger flavour (might help it move around inside a teabag too). Tea leaves are oxidised to make black tea (as opposed to green tea) and tearing the leaves is sometimes part of that process to speed up oxidisation.