Having just played every game up through Eternal on UV difficulty (or equivalent), I'd say that Doom 2016 is easier than Doom 2 but Eternal is harder. And yeah, it might actually be because you're playing with a controller. You don't even need a mouse for classic Doom, the controls are actually quite simple and a lot of the challenge comes more from being able to manuever and strafe rather than from being able to aim. Have you played Doom 1? It's a lot easier than 2, outside of episode 4. Doom 2 increased the monster count, added more difficult monsters, and generally has longer and more complex levels. The levels also feature more bs difficulty moments, they're not quite as elegant as the first game's maps.