They are not a disadvantage as far as bearing surface goes. More engineering crap that engineers loose sleep over.
What they don't say is they don't want oil to the rods all the time. Most engine builders are smart enough (or should be) to calculate area and most bearings have more bearing area than you ever need.
Sending oil to the rods full time takes more oil volume, so you need a bigger pump (not good) produces more oil exiting at the Rod bearings (bad) which in turn means you need more oil in the pan and a bigger pan to hold it (also bad) and lastly, you are trying to keep oil off the crank and dumping oil out the rods all the time is a big power eater. The higher the RPM, the more power it eats.
Full grooves in the main bearings is a fix, not a cure. Bearing area is the least of your worries.
I'm still trying, in my mind to understand how you think pulling oil off the 2 and 4 mains to oil the rockers made you lose bearings? The system is self regulating. In fact, if I'm running a high RPM roller deal, I open up the feed from the mains all the way to the shafts, and put a groove around the cam journal.
Years ago I blocked the oil to the rockers from the mains and plumbed up full time oil to the rockers. What a waste of time that was.
The Chrysler system is good for what it is. It seems to me you are doing a bunch of engineering based you don't need because of a failure you had. Go to the track and see how many guys are going through the hoops you are. I don't know any. I personally have never seen a main bearing failure from oil going to the rockers. Not one. Not even the big block guys who are 100% sure that's the failure.
So no, I don't think a full groove in the main bearing presents an issue as far as bearing area. As I've said it presents other issues.