I believe the "20% discount", per the MR website, refers to using MR points solely for UA miles; not for a travel package.
A travel package would be better than simply exchanging for UA miles.
You can exchange 224,000 MR points for 100,000 UA FF miles.
Or for 235,000 MR points (if you are a Marriott timeshare owner), you can get 132,000 UA FF miles AND a 5-night stay at a Marriott property (categories 1-5). That's 32,000 more UA FF miles and a 5-night stay for only 11,000 more MR points!
Or for 270,000 MR points (no timeshare ownership required), you can get those same 132,000 UA FF miles and a 7-night stay at a Marriott property (categories 1-5). Since a category 5 hotel reward for 5 nights costs either 80,000 (PointSavers) or 100,000 MR points, the travel package is still a great deal compared with just exchanging MR points for UA FF miles.