What's the context of the above discussion, especially as it pertains to Canada?
Are we talking about a fire support system to be held organic to a LIB or LAV Bn in the CS Coy, or an RCAC capability designed to be attached at the scale of a sqn / sqn (-) to add teeth/weight/mobility to an LIB or LAV Bn based BG?
My answers: Re- Organic DF- nonsensical, both battalions should have appropriate robust CS coys based on the overall weight of the unit - LAV based for the LAV, light/ ultra light vehicle or Man portable for the LIB
If we're talking RCAC- that discussion hinges on whether the above robust CS Coy's exist. If a LAV Bn already has turreted 120mm mortars and a DFS platoon mounting 50mmx228 + ATGM's UA, does a 40t with 105mm really bring a novel capability upgrade? Probably not- for the logistic juice to be worth the squeeze you're going to want an MBT. If that robust CS coy doesn't exist, there is a gap that an RCAC squadron in Bookers could help fill- but so to would an RCAC sqn in Jaguars or above LAV based DFS vehicle, with less change to the logistics footprint.
In terms of the LIB- the same premise exists- if you're going to send a Bookers, you might as well send MBT's. If you're not in the hyper specific scenario that calls for flying in a troop of MBT's to attach to light infantry, what weight/capability makes sense? If they have their version of a robust CS coy, you're going to want to add armor- not just more armed rascals, so you're looking at a range from something like the JLTV HGC to the above LAV DFS/Jaguar.
The Army needs to decide what the infantry is going to bring to the fight before it can decide what it needs the armoured to bring on top of that, and in what scenarios. The easy and obvious answer is "more tanks." But is the answer "only tanks", or is there going to be another capability gap that needs filled, and if so- at what weight?