Almost half the battle when putting a trio together is just how much noise you're able to make. Since there's only three of you, you're not necessarily going to be creating the same kind of sonic bombast that people like Slipknot can do with 9 members. What do you do then? You work outside of your context altogether.
Long before any heavy metal started coming to fruition, Lemmy was paving the way for the hardened side of rock with Motorhead, turning every single song he wrote into one of the gnarliest grooves imaginable. Despite people claiming they make the same song over and over again, there's a lot more variety across every lineup the band has had, from the punk tinged sections of Overkill to getting bluesier in their old age on songs like Whorehouse Blues.
Even with the changing lineups, it almost doesn't matter as long as Lemmy was leading the charge. No matter how many albums they released, you knew that there was going to be some baseline level quality to a Motorhead album. But what to classify it as? Some say this was the beginnings of punk....some say it was the sounds of thrash and metal a few years early. In the man's own words, Lemmy always said "We are Motorhead and we play rock and roll." And that's been more than enough for all of us.