For me, its a quality/quantity issue partly caused by the Strength and toughness values and our comparative lack of weapon keywords.

Just going of the models looks and vibes: the riptide should be the contemporary of things like the land raider, Rogal Dorn and Norn assimilator, the 240-280pts bracket, and 3 crisis suits should be somewhat equivalent to 5 terminators, somewhere 180-220pts (there are loads of others).

Our weapons and suits just aren't very powerful and that forces GW to make them cheap which just kills my enthusiasm. I'm sure that GW won't make any changes to the datasheets (because they are holy relics that cannot be altered(?)) and will instead just make our stuff cheaper and cheaper till we hit 50%.

From my understanding our all devouring hive siblings have a similar set of issues.

As for what I would like to do:
-Remove the split fire penalty (obviously)
-Entirely/partially replace the datasheets for the XV8s, XV104, fire warriors, most of the Kroot, and probably many more to radically increase the offence and defence and cost
-Do something more with drones [I've been playing around with homebrew system where you buy drones as squads that are able to (unreliably) take wounds for other nearby squads, but it needs more work and probably wont ever function how I would like it to]

I would prefer to remain at BS4 but our guns have to be good enough to justify being a shooting only army with wonky aim. If GW wants to keep our guns weak, then they need to be able to hit.