I like where a Rogue dip can be really useful for Monk, but it's not required to function. Let's look at the impact of delaying your Monk progress by 1 level (and bold the winner)...
Monk1/Rogue1 vs Monk2 - multi doesn't have Ki abilities (but is a goddamn terror with 3 attacks + sneak attack)
Monk2/Rogue1 vs Monk3 - full has subclass already (and Deflect Attacks omg)
Monk3/Rogue1 vs Monk4 - full gets ASI/feat
Monk4/Rogue1 vs Monk5 - full has Extra Attack (and Stunning Strike)
Monk5/Rogue1 vs Monk6 - full has magical hands
So the Rogue is unquestionably ahead on lv2. At lv6+, when Monk is no longer getting something every level, the Rogue Monk is mostly just losing out on 1 Ki, so this is another time where they are likely better, but by this time, an extra attack (plus 1d6 from sneak attack) isn't as big of a deal.
Expertise is pretty damn tempting, but at least Skill Expertise exists if you want it for just one specific skill.