On the subject of saves, Rogues have the third best spread of defenses (monk at second barely, and Paladin in front by a full country mile)

When slipery mind comes online they have
Dex, Int and Wis
With Resilient they can take another, in optimized crowds this is usually Con

So they have proficiency against all 3 major saves, and 2 of them will tend to have significant investment (Dex and Con)

Along with evasion which will no sell a bunch of dangerous damage effects, save wise defenses are pretty good, heck they will trend better than monk since they are less reliant on feats for optimized damage lines, and resilient is not a dead pick by high level. Monk only passes a the 14th level point because Strength and Charisma saves will sometimes matter.

Oh and the One D&D stuff is looking to give them Charisma save proficiency as well as Wisdom. Which if that makes it through will make this argument stronger.