As of 14 May 2017, the revised ranger has not been balanced for multiclassing. I'm looking for justifications, both balance and RAW, for allowing or banning this.
The Revised Ranger's beast companion "uses your proficiency bonus rather than its own"
The Rogue's Expertise class feature says that "Your proficiency bonus is doubled for any ability check you make that uses either of the chosen proficiencies."
What will this break, if anything? The worst thing I can think of is a +8 STR(Athletics) check on a grapple at level 5, but a Valor Bard can have the same bonus and Extra Attack at the same level.