Indirect fire support needs to be centralized to be flexible. It's nigh impossible to take a resource organic to a battalion and apply it outside the battalion's AO. Indirect fire support needs to be able to switch priority of support, without endangering our own troops, at a moments notice.
I think there needs to be distinct boundaries on what are organic assets to a unit/sub unit and what a supporting assets from higher. Flexible for some will be inflexible for others.
The three CS Bty for a Bde makes sense when you have 3 maneuver elements. They can be allocated as needed, but generally that was the reason the BC’s were out with the Bn’s so they could have ‘their’ battery if needed, but the Mortar Platoon was the the only true organic IDF asset the Bn has.
I am a big fan of 3x 8 gun Bty’s for the CS Reg’t mainly as it can allow for a troop to over watch while another moves, but also it gives the Bde 24 tubes which I think is the bare min to cover the needs of the commander*
The GS unit from higher supplied the CB fire. For that I think HIMARS and MLRS check the box. I like the additional rocket ability of MLRS but given the range, the tracks don’t provide any more needed mobility, as it’s not up crossing with the A vehicles.
I always liked the idea of the 120mm Mortar (preferably vehicle mounted) for Mech units. As it can put significantly more weight of fires than the 81mm.
The 81mm I would limit to Light (Airmobile/Para) units.
Now why I like the Spike NLOS ER, and putting them under the Bde Cav, I subscribe to the US style Cav setup, and it provides a precision strike capability to support their actions, to which I’d also have the 120mm Mortar support there as well.
With the ABCT or Armored Div’s the CAV are a sense and strike unit that can also screen as needed, in the Lighter Units they have enough firepower to extract under contact from heavier units.
*24 155mm is on top of Bn and CAV Mortars, as well as AH and CAS etc.
Frankly in the CA context, I think a CS Reg’t probably needs a lot more due to the lack of those support systems.