In my view, a LOT of believers misread this often quoted scripture. Look at it again.

For we do not wrestle against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places.

so, NOT against flesh and blood, BUT against principalities, powers, rulers (of the darkness of this age, against spiritual hosts...

IMO, it's not saying that the struggle is purely "spiritual" aka only to do with the spiritual realms. What it's saying is, it's not the muscle in the street (aka flesh and blood) but the rulers, the wicked elite who control the world in addition to the wickedness in heavenly places (aka the spiritual realms).

So, yeah, its spiritual struggle, but it's not just against spiritual beings in the spiritual realms, but also against living beings inhabiting the physical realm as well. But we fight them with spiritual means.

So the struggle is two-fold: one, against spiritual beings aka spiritual warfare, but also against the evil power centers that rule the world (Satan is the god of this world), rulers dwelling in the physical plane.

The tools of the struggle are primarily spiritual, but we're battling evil both in the heavenly realms (spirit) AND in the material realms (principalities).

Least, that's how I understand it at this point.