It’s very common that waiter tells you we have Pinot Noir or Merlot, but without telling you at least from where they are, that information is pretty much worthless. And I’m almost sure most people can’t tell the difference anyway.
I’m a lifelong wine lover, even with some education in wine tasting, and the more I know about wine, the less I’m sure I’d be able to tell them apart in blind tasting. It’s more like I roughly know what style of wine I can expect from different countries, and which varieties have good conditions in those countries and which are better avoided.
Do some Merlots taste more like Cabs? Sure. Is an experienced wine drinker going to mistake Pinot Noir for Sauvignon Blanc, even if they’re both from Sancerre? No way.
> There’s no “better”.
To nitpick, there are definitely better and worse winemaking grapes—thing is, the bad ones are only grown by necessity, as in the case that the better ones won't grow well due to e.g. weather, so for obvious reasons they only tend to feature in wine from places that aren't known for winemaking.