It has the effect of nullifying the bike part. It's so much easier to just "hang" with a group than go it alone. So if you get out of the water with a "good, leading group" then you can hang with them even if you are a lesser cyclist.
Everybody then in the bike part will want to conserve energy for the run.
So the game becomes, "hang with the main group for the swim" so you can get out of the water with them, then it becomes "hang on to the lead group" on the bike leg (which is demonstrably easier if you suck a wheel). Then it all comes down to the run.
Personally, that would favor me cause I happen to be a relatively strong runner.
But surely you can see why drafting can be such a game-changer on the strategy. If you can draft you are going to change your game for that. If you can't draft, you are going to change your game for that.
And some folk don't have the depth to change their game-plan as they don't have enough strength in all three sports.
And, to me, the idea of a triathlon is to be competitive at all three sports.
You know how folk whine about sit-and-kick. This is basically the same argument. Cause it's a TON easier to "sit and kick" (focus on the run leg) if drafting is allowed.
I think, overall, it's a discussion about "what is this sport". Because if triathlon is a sport about three disciplines, then let it be as equally as possible about all three disciplines.
Of course, the big problem is enforcing drafting rules.
So, that's why there's such a huge discussion around this. That's why they are such "tightwads" about drafting. Because 20% is nothing to laugh at and it changes the whole sport whether it's allowed or not.