Thanks...
People buy instruments for many different reasons, and those reasons change not only from country to country, but each city has some specifics because different music is played, furthermore we all have our perception of reality, and our own taste. This is not just about factory styles, and sounds, but what keyboard can do besides that, editing capabilities and peripherals such as vocal processors, speakers, keys, buttons, etc.
For example, in South-Eastern Europe and Middle East people usually buy Korg Pa, in Western Europe they mostly buy Yamaha, Roland E-A7 can be found in Philippines, Indonesia and that part of the planet, while across both Americas the situation is little bit more mixed. This is not some general rule, just what I noticed over 10 years of working with people all around the globe.
For South-Eastern Europe and Middle East it is important for keyboard to have powerful editing because 90% of factory stuff is simply ignored. I understand this maybe sounds strange to you, but this is reality. In those cases what is really important is powerful editing, RAM memory so people can use custom made sampled instruments, and drum kits, and above all custom made styles. And here you have the main reason people buy Korg Pa, yes it does not sound as good as Yamaha or Roland, but it is well made, it has powerful editing, a lot of RAM these days with ability to compress 16 bit data, now it has disk streaming as well, and it is full with features people like, TC Helicon and other great peripherals.
With that being said, not all custom sampled data they use is of good quality, in most cases it is not, but what is important is the manner they get with that sampled material, suddenly the music sounds familiar, the sounds sound familiar, then they have what they want and factory stuff is irrelevant. There is also Korg's ability to create many different scales, to make real thirds, advanced portamento, and much greater sampling and sound editing capabilities, more open system, Korg is the right choice of course.
One more thing about Korg, many people I know simply do not like "CD like quality" of Yamaha, they want something more "natural" as they say, something more like "live band with all its flaws", something that sounds more raw.
As for Roland E-A7, well it is not very popular keyboard nor it exists for too long so there is no consensus about where it belongs because it is Roland's comeback to arranger market. This is very strange keyboard at first sight with those two 90's displays, however the way it reproduces the sound is simply magical. I am not religious about my equipment nor in general, so when I say magical I mean it sounds subjectively good, but it can be translated to numbers and measuring units of course. It has internal +6db and +12db amplification for imported WAV files, so when sampling you do not need to use limiter to crush audio files in order to get the same RMS as factory ones. This makes the files sound thick, and full, without crushing low frequencies, drums can retain their natural transients, and sustain of the instruments sounds more natural. Other than that, each time you use that amplification the keyboard applies very soft internal limiter to each sample, so you end up not only with much greater quality WAV file because you did not squash them with limiting to achieve high RMS, but you get internal soft limiting fo each sample individually, which produces some really magical results.
All this together with MakeupTools makes this small and affordable keyboard much better keyboard for me personally because I use high quality sampled drums and instruments far better than any factory stuff in any modern arranger, so for anyone who want to use custom sampled sounds and drum kits, and then the results get much, much better than any other keyboard on the market.
And that is the answer to your question, it is much better than Pa700 and S-775, and much worse at the same time, depending of what you need, what are your plans, and what are your expectations. But when it comes to ROM base, it is in the middle between S-775 and Pa700 for me personally.
When it comes to ROM base, for me personally styles, drums, strings, acoustic guitars are the best on S-775, piano, rhodes, distortion guitars and organs, also great Makeup Tools on E-A7, and as I said earlier great editing and other capabilities are best on Pa700.
You mentioned realism, well it is very subjective category because we all have different lights in our heads turning on when we say "realistic". For me personally all of the keyboards mentioned here do not sound realistic. Far from it. I hear it is a ROMpler after 1 second of listening, while after 2 or 3 seconds I recognize whether it is Korg, Roland, or Yamaha.
However you are right, if we talk only about ROMplers Yamaha indeed has the best ROM base, and their way of sampling, attention to details, and realism is not matched by any other brand. Besides that it sounds good right after you take it out of the box so it is understandable people like it and with a reason believe Yamaha makes great arranger keyboards, which is true for most people because most people do not use any custom sampled instruments and drum kits ever.
Long story short, there is no right or wrong here, it all depends of what you need of course. But one thing is constant, there is no need to be apologetic about any brend, because we customers want the best for our money.
We want better ROM base from Korg, we want higher grade arranger from Roland, and we want Yamaha to be more open about their OS, and more user concentric, to give us abilities to create content, to be more creative, and of course to use their keyboards faster and with more logic.
This is not a blasphemy, we can say it loud, and we should.