I'd be happy to elaborate.
A pure game of Diplomacy would involve no records or ratings, but most people (including myself) enjoy keeping track of such things. With a game such as Dip, it's hard to find one system that accurately reflects how a person plays.
W/L/D ratios are nice, but don't reflect the skill of your opponents. GR is nice in that regard, although it has some flaws (which I've discussed ad nauseum). Overall, I think these both do a decent job of reflecting a players skill at Diplomacy.
What do points indicate? How good you are at getting points. Point farming is an enormous problem. Let's say I wanted to farm some points. I could play with 6 noobs at 100

each and if I win in a WTA, I would increase my points by 100%. What nonsense is that? My wins would only increase by 1 and I don't think my GR would change at all. This is just one example of the many ways people can scam the point system.
Now, you might say: who cares? Let people farm points. Here's why you should care:
People like having the most of things, even if it's stupid like "points" on a game. They will play in odd ways (such as handing away a solo in a PPSC). This is a problem because people who don't know what points are (because they've been playing Dip for 40 years) or don't care about points have no idea what's happening. When people go into a game with a different opinion of what is "winning" it doesn't make for a fun game. Not to mention, imho, points are clearly metagaming.
Does that help to clear up my position?