I might be incorrect but I'm pretty sure Disney didn't move MNF from ABC to ESPN until 2006. Which, I'm also pretty sure, was the year NBC's Sunday Night Football started.
Here's the thing. The NFL made a very deliberate choice to tank Monday Night Football all by themselves in order to prop up their new darling, Sunday Night Football.
Once the NFL's mind was made up to give the Sunday night package to NBC (after years of it being a pretty mediocre game on ESPN), and to build up Sundays at the expense of Mondays, I think Disney made the right call for themselves in moving MNF from ABC to ESPN. Did it cheapen the MNF brand? Sure, but that brand was about to be pissed on by the NFL schedule-makers anyway. This way, they did ESPN a huge favor by keeping them relevant with live NFL football. Considering how things have played out with video on the internet in the years since then, they've been proven very right. If they let ESPN lose live NFL games and counted on staying relevant simply because fans needed ESPN for highlights, they'd have lost that gamble in a big bad way.