OMG I'm confused! Just sat and read the whole thread and it seems like everyone agrees but is somehow still having an argument about it?
It looks like everyone agrees there are two ways of improving, either the rider (training/diet etc) or the bike (upgrades/lighter parts etc). This of course doesn't mean you have to choose one, you can change both. If for whatever reason you don't want to/no time/inclination etc to train or calorie count then you may just work on the bike side - a decision which costs you money, but as it is YOUR money it is no one else business to say if you're right or wrong in doing so. Similarly if you are happy where you are and aren't constantly trying to improve/strava etc - there's not many of us on here who are in serious training, I understand we are large hobby/commuter cyclist and whilst it might matter to us there's no real world effect of us being 1mph faster or slower than anyone else. Obviously if you do want to improve and have the time and money to attack the problem from both ends, e.g. improve rider and improve bike then your results will be better than those who do one or none.
Surely it is pretty obvious that if you put the same rider on a heavy unsuitable bike and a light suitable one he would be quicker on the lighter 'better' bike. Similarly if you put an average rider and a pro rider on the same bike the pro would be better. If we take both of these, the winning bike and the winning rider, we get the obvious answer.
I can't believe people are arguing and name calling about this. Have I completely missed the point somewhere?