What can I do to improve that? Accent the second stroke on a slow tempo? I don't see the knowledge behind that because at a faster speed ill mostly be using fingers and rebound control as opposed to making a strong stroke with my wrist
No, I don't think you have to do that. You've got enough finger control to stick with quicker tempos, it's just a matter of refining it. I would back off on the tempo and work on the doubles as 16ths from around 108 BPM or so. When you're playing a Long Roll, rather than hearing your hands as two seperate entities, try to hear the notes you're playing in longer strings of 4 or 8 notes or even more. Trying to make every one sound exactly the same. Gradually push the tempo up. Oh, and resist the temptation to slightly accent the first note of whatever length you're counting/hearing. Record some Long Rolls at various tempos and listen back to hear where things get uneven.
Use shorter bursts - i.e. 4s, 5s, 6s, 7s, 8s, 9s, etc. of double strokes trying to get every note to sound identical. I.e. don't accent the last note. Like I said above, try to hear each group as a continuous whole. Oh, and make sure to do this leading with both hands.
You can also try playing your doubles inverted and accent the second note on the downbeats and/or the
ands. That is, start by accenting the second note only in one hand. Then switch your lead and do the same, then add in the accent on the other hand. This is really good stuff from about 120 BPM up in my experience.