At least the stuff I like (if it would actually be called ‘drumstep’, which I’m not certain about) is generally quite a bit slower than drum’n’bass.

Depends on what you mean slower. Drum and bass is in the 160-180 BPM range. Halftime is in the same range, but the drums are slower -- typically the snare hits less frequently.

Is that not what drum’n’bass is doing, too? I don’t think I’ve ever heard a drum’n’bass track that wasn’t halftime with some kind of two step pattern.

Drum and bass is typically 2-step, but not halftime. For example: Lost Friends by Halogenix is classic 2-step drum and bass, but Orange by Halogenix & Two Fingers is halftime. Both tracks are in the 170-175 range, yet they sound quite different. Both are considered drum and bass and easily mixable with each other.

The two tracks you mentioned in your other comment are both halftime. One is 160 BPM, the other is 172 (I checked in Mixxx). That is drum and bass territory. If they were slower, around 140-150, they would probably be classified as dubstep. To be honest, genre labeling doesn't really matter because producers tend to experiment a lot. But you'll have much more success searching for "halftime" than "drumstep" for the style you like.