For suspension parts, it's an MT09 front and MT07 rear right, this is not entirely new design. My suspension guy told me, Just let me know when you are ready and how much you want to spend, we'll put it together. I'll probably eventually go GP in the front, not sure about the rear, most likely Ohlins. He'd be putting it together and dealing with any setup issues, but that is what he does. For now and for my immediate purpose, it is set up for me fine and I like the way it rides. Stock springs are about at their limits but the numbers are fine for now. I doubt I'll get seriously into road racing now but it has been and will be on the track so at some point the suspension components will be changed, probably when the springs wear a little bit.Similar to what SetemberToob says. A) Many of these parts aren't even available yet from many of the aftermarket msg's. B) Compatibility, if you've ever built a race bike you learn that when you source from different mfgs you can run into conflicts (Exhaust is an example, if the bodywork is cut out for the Akra pipe and you get a Yosh, you may have to modify). Similarly sometimes the exhaust may try to use a mounting bracket that the rear sets required you to remove, on and on it goes.
There's no clear answer these are all personal choices. The ignition bypass for me is a critical one and I've done it manually before, but I'd much rather buy a switch guaranteed to fit the OEM triple and plugs directly into the wiring harness. Handlebar switches same thing, I don't feel like researching and buying individual waterproof momentary switches and hacking harnesses. So when Yamaha themselves do the engineering and offer all the parts together I can just buy them all from one supplier and they all are known to work together.
Money is the big reason not to go this route, you can save a few bucks hand picking where you want to spend more or less to fit a budget. For me personally the time is far more valuable than the slight savings so I'd personally prefer to just order it and not have to worry about it or figure it out. Parts arrive, they get bolted on and I'm back on the track.
Just my $0.02 and all of this again is personal preference and priorities but those are my personal reasons for wanting to just go to a GYTR Supersport page, add all to cart (except bodywork) which BTW I'm confident will be Sharkskinz bodywork. Hopefully I don't offend anyone with my response I'm just sharing my personal perspective, opinion and experience. I used to race an SV650 first gen many years ago so I know exactly how painful it can be when parts being used aren't "designed" for the bike. They work for sure, but I'm too old now to be dealing with that. Exactly why I bought the R7 I knew they'd put together a package that I could just buy and throw on and it's ready to go. The track time and using the bike are where I want my available free time to be spent. There is NO wrong way to prep a bike though. Heck, you can for track use just tape up the lights and call it a day. I've done it and there is nothing wrong with that at all.
I do like your plug and play idea KDE, I may end up doing just what you are saying. But then I am wrenching, which I typically don't mind, but if I don't have to, that's more time for me to do other things. And since I don't really have an off season, it will get done faster if I have my mechanic do it so I can get back to riding.