I can't fully defend Outlook, but I do believe many serious professionals use it, limitations and quirks and all.
I am curious, though- what email client do you recommend instead of Outlook or other "poorly designed, poorly executed, feature lacking, functionality lacking email clients"? I have been looking, use Thunderbird myself (its basically OK), but I don't see a lot of great stuff in the "email client" space. I'd love to be wrong, though.