Lindsay, I didn't mean bad writing for Matthew and Mary in the first seasons. I actually love them in the first seasons and think Fellowes did one of his best themes with them there. I meant failures in terms of writing for the show, in general. For me the first 3 seasons for Matthew and Mary were favorites (with few exceptions like the jumping of the wheelchair but that's not a deal breaker) and that's why I watch them again and again.
But overall, there were plot and writing problems and I truly think Fellowes has major problems writing both happiness and deep sadness.