I tend to agree with you. I am on my second boat the first one had a Merc (6 cylinder)(Tower of Power)never had any problems with it at all. My current boat also has a Merc and the only problems were the rev limiter went on it and the oil monitoring module. The same with the kickers that I have had - zero problems. Now I do look after my equipment and I am sure that comes into play when it comes to problems. The only motor that I would shy away from is the Evinrude "Ficht", mind you I am sure there a guys out there that have not had any major problems with the "Ficht" model.
Personally I would not have any concern with the Yamaha. Just make sure you have a competent Yamaha mechanic to service it when the need arises.