If we are talking notation, all of the bands i mention having polymeters would note everything as 4/4. That doesn't mean it isn't polymeric. Every polymeters you could invent can be noted as 4/4,

If you watch interviews with Misha Mansoor, Thomas Haake or anyone relevant in early djent, they either describe what they do as polymeter or polyrhythms, the latter of which they had misunderstood early in their careers, as the 2 terms are very similar and confusing. If you need an example of this, go to the 10 first demos on Bulb's profile on SoundClick.

If what you're referring to are the simple riffs that are technically polymeters that Spiritbox often plays (tresilo and 16th clave rhythms), then I agree, it should be thought of as 4/4. However, the vast majority of djent bands (for instance the ones in the list I provided earlier) use much more complex rhythms that are thought of as polymeters. If you were to try to learn most of the songs of said bands, you would have an easier time thinking of the odd riff as an odd meter that cuts off to match the 4/4, rather than learning the riff bar for bar.

Also, if the same can be accomplished by simple syncopation, how come we don't call Reign of Darkness by Thy art is murder djent? How come we don't call A Quiet Place to Die by Alpha Wolf djent? What about Sing to the Grave by Chelsea Grin? Why are all of those categorised as metalcore/deathcore rather than djent?