Tony Vargas
Legend
Party composition can radically change the number of attacks a party of 4 can make in a round. The real issue that might distort CR considerations (not that CR is terribly precise to begin with) would be one of overall DPR, which such abilities needn't vary to any greater extent that is already likely with varying party composition.Attack support will be difficult, because CR (such as it is) is based on the notion that a party of 4 makes X attacks, not X+3 or X+2 if it takes the recipient's bonus action.
The stumbling block there would seem to be the de-coupling, in 5e, of attacks and actions. An action might be a single attack, or several attack rolls, or none (but still do damage automatically, on a failed save, or even on a successful save). Still, hardly seems insurmountable.