Imo the spread works pretty fine enough.
[Insane] was mapped as one of the mapping styles in 2012; slow sliders and large distance. By that, it's giving both relaxing section and a high tension section in the map. The star difficulty gap is pretty larger than normal-hard when it comes to hard-insane, but it shouldn't be the sole factor judging the spread. The reason why the star difficulty of Insane has got higher was that there were pretty massive jumps like 01:30:771 (4,1) - 02:29:632 (1,2) - etc. The rhythmical composition of Hard and Insane are pretty similar, but the major reason as you could see what made the gap is the jumps. Maybe adding some more jumps in Hard could be nice if you think there's a spread problem, but I think the 1/2 note clicks already construct one difficulty aspect, and the 1/2 sliders with big distance such as 01:20:328 (1,2,3,4) are already portioning a good ammount of jumps. Perhaps the small distance of 1/2 notes in Hard was the one bugging you, but considering the current bpm is 158 anyways, those constant 1/2 clicks are never something simple and never also boring. Hard is securing it's difficulty with rhythms, and Insane is securing it's difficulty with larger distance based on the rhythm of Hard.
Again, personally this is an acceptable spread which gives users enough various difficulties to play. Giving the mapper the need to close that gap whether by asking to add an additional difficulty, or to do some reworks for Hard just seems too much compared to the issue.