@UCIMBZ +1

There is play, there is flex they aren't related to one another.

Older wheels and some new designs let you adjust the play. Many of the new designs (assuming the 5mm bolts are snug already), the only way to remove the play, is to take the axle assembly apart and put a small shim into the assembly.

Generally once the wheel is loaded, ie you are sitting on it, you'll find that play disappears and is not something you should be worrying about or even thinking about.

Wheel flex, entirely different, it's no fun climbing or cornering with your wheel flexing and hitting the brake blocks. Is there really any way to objectively measure flex? Not really, you can put the wheel in a jig and hang a weight off the rim and measure the deflection.

At the end of the day humans are very bad a 'perceiving' things, and as individuals our perception tends to vary wildly etc. Having said that, if you aren't happy on the wheels, you aren't happy and unless you can get the notion out of your head they are flexy, then thoughts of them will probably continue to occupy your riding time. I've switched out plenty of stuff just for placebo cause for one reason or another I wasn't happy, including high end wheels.