Dropping in to say thank you for the shout out 
and give my (biased) opinion. Full disclosure as you know - I sell OSR2+s, so please take my opinion with a BIG grain of salt.
I find multi-axis SO important. No matter how good a single axis stroker is, it still feels extremely robotic to me. There aren’t many sex acts that follow a perfect linear axis - pretty much all of them have uneven pressure or motion, even if it extremely slight.
Having built about 10 SR6s in my sexbot tinkering career, I have a really hard time recommending them to most people. They have nearly double the amount of potential mechanical failure points and are much harder to assemble and repair. Additionally, active cooling is almost required, as the servos are packed so tightly, there isn’t much room for passive cooling. Double the # of servos is double the amount of noise too. Also, like you, I found that the “surge” didn’t add a whole lot to the experience.
However, it’s not all bad with the SR6, the weight of your sleeve is distributed across more servos, which hypothetically would lend to longer lifespan. I would still recommend SR6s for people that use heavy sleeves and use extremely intense scripts.
I find the OSR2+ to be the best balance between extreme complexity and simple and serviceable design. They’re much easier to work on and repair. It still provides a VERY good multi-axis experience with less noise and cost. I would take an OSR2+ with expensive servos over a SR6 with cheap servos ANY DAY OF THE WEEK. Moving between my SR6s and the OSR2+, I don’t feel like I’m missing much, where as moving between my OSR2+ and the Handy, it is unbearable
As far as twist and the valve, definitely not worth the added complexity, noise, and weight. There are passive valve caps you can screw onto your Fleshlight if you really like that suction sensation. I know that some people SWEAR by the twist, but I really am not in that camp. I think that the concept is SUPER intriguing - to the point that I build myself a twist every time there is a design revision - but they never stay installed on my unit very long.
So long winded way of saying OSR2+ is the right amount of axes in my humble opinion. Not a sales pitch at all - there are a lot of great OSR2+'s out there. I just think it’s the perfect intersection of performance and simplicity.