I agree that the entertainment side is why a lot of people watched Attitude Era WWF, and it was unpredictable (something TNA can never truly be whilst they tape shows in advance), it was also, barring a few ridiculous storylines, well written and exciting.
But apart from a few - Undertaker, Big Boss Man to name two - WWF was crawling with young, fresh talent who were exciting and who the crowd could relate to. Would the Attitude Era have been as successful if WWF had used wrestlers 20 years past their prime in main event spots?