Yes and no. There's an important distinction between _having_ something and _owning_ something. You can have possession of figures carved from contraband elephant ivory. But if anyone who was inclined to care about such things decided to take action, a court could compel you to destroy it. Same thing with any illegal item.
But these are all "ifs and buts." Hence why it's a matter of principle and not practice. At the end of the day, most people are fine with "buying" a book that they don't own as evidenced by the sales.
most people are under the impression that they own the things they've paid for, and the inevitable rug pulls always take them by surprise.
rejecting the bullshit rules of rent-seeking parasites would be a more worthy principle to pursuit.
Second, strip the DRM using Calibre, and store the books off any cloud-based platform and on your own drives, as you always should in any case given the proclivity of many content companies to just flagrantly bullshit their way into excusing themselves when they frequently steal back their customers access to stuff they ostensibly own.
Once a piece of digital content is actually yours, in your own device drives, it's only then really yours.
Keep the on-device cloud-based versions around if you like the user interface of your platform or reader, but your own digital copies elsewhere. The retailer doesn't even need to know (though I personally wouldn't give a tin shit if they did anyhow).