I'll hazard the guess that it's probably both the toner and the printer.
Toner from those off-brands, in my experience, is not a prudent option. A false economy, IMO, as gleaned from several vexing disappointments. I don't care about others' favorable experiences, there ain't nuthin' like OEM toner for the best results in a given printer, and especially in an HP.
My HP 4MV finally succumbed last winter after (at least) 17 years and many bundreds of thousands of copies (2 offices have graced this household at one time, one still does). I hated to replace such a workhorse, but doing so was a revelation. They don't make them like they used to. They make them better.
We are delighted with the quality, characteristics and even the price of its replacement. It's an HP tabloid printer and its a jewel . . . HP knows its business.
Of course I remember my first dot-matrix AppleWriter printer, including every pound of its iron frame!. I'll bet it's still chugging along somewhere, like some of the DC-3s that are still flying in the jungles of the world. It just that I wouldn't want to be "using" it, or them, these days.