I totally agree that when it comes to reliability and consistency the Shapton GS are as good as it gets. I have done several thousand razors on these stones and the bottom line is that they work. I also like the HC stones in the 4K and 8K and they work their way into a rotation without problem. I have never had the success from other Shapton stones that I get with the GS.
I think the biggest problem in doing the heavy Sheffield's on them is that most of the Sheffield's around today have significant and uneven hone wear that may not match up on both sides of the spines and edges of a given razor. The Shapton GS are to me, the hardest of the synthetics I use and I find that the unevenly flattened spines tend to catch or skip some on these stones.
The current processes on these stones is very learnable and repeatable for new guys and if you do decide to hone more than a few razors, you will not figit with these nearly as much as some of the naturals or other stones out there.
Keep in mind that there is a lot of personal preference, mindset and people loyalty associated with sharpening stones and honing. What is available to us both in media and technique or process has grown a lot.
Norton is still a very consistent hone particularly in the 4K/8K and if you like abrasive for setting bevels and repair 220 and 1K too. Naniwa Supers are very comparable to me from a result standpoint with both Shapton and Norton although they have a softer feel and seem to be less abrasive to the spines and yet have great cutting power. All have a different feel and feedback to them. There are some great natural stones out there and again to me and keep in mind that I use them daily are can do stones and usually do not have the same amount of consistency. But, if you are just a hobbyist and have the time to play with just a few razors, they are a ton of fun.
The one thing that we really don't talk about much is comparing the Naturals to the synthetics purely from a refreshing standpoint, but I know someone will start a thread on this. I think this is where the naturals can shine although the synthetics also are excellent. As Jimmy often says, once you learn how to get a shavable edge off an 8K, you are well on the way to really learning this art.
Bottom line is that a set of Shapton GS stones will last a lifetime for most people and you really will never NEED other stones.
Have fun,
Lynn