5 Membership Rewards points is not the same as 5 percent.
Membership Rewards -and- Ultimate Rewards points are both worth more than $0.01/point. You will need to work out the value of each based on your individual redemption profile. If you were to open the Charles Schwab co-branded version of American Express Platinum the points would have a minimum value of $0.0125 each, which means 5X = 6.25%, but you may do better transferring points to airline partners.
As far as transfers are concerned, MR and UR are kind of the same to me as they both have many partners. So whether I value a "mile" at .01 or .02, it is apples to apples.
Regarding the Schwab cashout trick, that is a very valid point, but I still don't think that it tips the scales toward MR vs. UR in my example above with Expedia.
CSR with Expedia: 4.5% UR + 1.4% expedia rewards + 6% topcashback = 12%
Amex Plat with Amex Travel: 5% MR. Even valued at 1.25x this comes out to less than 7%.
I love the Plat card side benefits but surprised at how poor they designed it as an actual spender card. Even for it's target categories it rarely makes sense, although can see argument for booking airfare with it esp. with Schwab cashout over CSR.