You can fly most things with a CPL, as an FO - provided that you have a rating for it
Not quite.
In answer to your question, you stand to operate nothing in the airliner world without an IR.
Bear in mind that 99.9 percent of commercially operated flights around the globe are flown under IFR, your CV without an IR is going to get filed in the tray marked 'SHRED'. . . .