I can't really think of a way to get the vroom levels totally standard unless one toy or a set was picked as standard. I don't think that would ever work, because it would exclude newer reviewers and plenty of seasoned ones who might not have the same tastes.
When I write reviews, I try to compare the vrooms to other toys. MiMi is my gold standard for a top level 4-vroom. However, although the Fresh was a teeny bit weaker, I didn't feel it was a full drop to 3 vrooms. Thus, Wiggle Room.
And as I said, the 1-5 has wiggle room. The Hitachi is NOT the standard for a "5". Some might use it as such, but it's not universal. Stainedclear, a reviewer I love, doesn't include wands in her 1-5 scale and says so. Wands are superpowered and no other vibes are going to touch that.
I don't have the Hitachi, but I have the Fairy and it's stupidly stronger in raw power than MiMi, yet MiMi is about my top cap for "normal" toys so far (Uma is a wee, wee bit stronger). I am never going to find THAT much power in a not-massager.
I use the description that Eden provides to rate vrooms as well, just like I do for bees.
1. Very mild, extremely low level vibration, great for newbies, foreplay and extra sensitive areas.
2. A lower-level intensity that provides light stimulation but can be still felt in most internal and external spots.
3. Moderate vibration, good for overall body usage, average in intensity and probably suitable for most individuals.
4. Strong and easily felt vibrations that powerfully stimulate but are not "earth-shaking&qu ot;
5. This car's outta control! Extremely strong, highly intense powerful vibration, probably too intense for most.
Those descriptions make vrooms subjective. Why ? Because anatomy differs. And so does experience. Not to mention different frequencies and types of vibration feeling stronger. Like the question "Is the Eroscilator a 5 vroom toy ?" You can look at it different ways and everyone will have a different answer.
I wanted a strong toy, so I read a lot of reviews and read different points of view - both from people who thought a toy was strong, to those who thought it was weak. I imagine if a standard was picked, everyone would disagree anyway, because people do physically experience the sensations differently and THAT makes it "subjective" no matter what unless you gave everyone the same anatomy. It might be the pitch or material or the toy being a certain size in relation to someone's parts, there are too many factors.