Okay, I have turned a corner on the commercials-with-golf on the same screen view. I just got to see Tony Finau and Tiger Woods make putts during an AT&T commercial. I don't much care for AT&T but their commercials are fantastic.
If it helps, think of course rating as allowing for fractional par. A 270-yard hole and a 435 yard hole may both appear on the scorecard as a par-4, but I would bet that in most circumstances, my average score on the former is lower than on the latter.
Par is also useful to track where the professionals are during a round when they've played an unequal number of holes.