It's not so much the fairing or lack thereof as it is your seating position on the bike.This leaking you speak of happens on unfaired bikes in heavy rain especially if puddling occurs..
Put your one piece suit on and sit on the bike. Look down. How does the material around your crotch fold? If the folds create a pocket with the zipper at the bottom of the pocket the suit will leak. So called waterproof zippers only delay the amount of time before that happens. You can often re-arrange the folds such that the zipper is not on the bottom of a pocket. If you do that you are much more likely to get to your destination dry.
However, beware moving around on the bike. The folds can rearrange, leading back to zipper on the bottom.
When I owned an RT the seating position naturally led to no leaking. On my GS I have to consciously move the folds around and remember to check once in a while when moving around in the saddle. Or wear my Darien/AD1 combo. If it starts leaking it's time for repair or replacement. My last Darien lasted about a dozen years before that happened.