Apologies for the lengthy post, but just recently I was analysing Russian and Ukrainian arty units and this piqued my interest. Hopefully it's helpful.
Each Group Army Artillery brigade has 6 battalions minimum (combination of 2/4 Howitzer and 4/2 MLRS ).
I would also like to see a source for this claim. The structure you described is extremely unusual for an artillery unit. It seems counter-productive from the point of managing operations and executing fire missions.
An artillery brigade is a corps or army level support unit, and with some exceptions as a division level unit - typically division level support units are regiments. However support units don't work the same way as combined arms units (infantry / armor) and they don't grow in size between echelons i.e. an artillery brigade or division (traditional name for army level unit) is not necessarily larger than an artillery regiment. The name indicates its
organic level of subordination within the hierarchy of command. An artillery battalion is subordinate to brigade hq and
not division or higher. Division hq issues orders to brigade hq and the brigade executes them on its own terms. If division hq has need of artillery support it has its own artillery regiment or brigade. Similarly corps and army have their own organic units for when they need to execute a fire mission or reinforce lower echelon artillery.
Six battalions of artillery is too many units. The logistical train for artillery is
massive and every battalion needs a separate train at battalion as well as a train at brigade level.
It's also too much fragmentation of structure.
Typically every battalion has 2 or 3 batteries of 2 or 3 fire platoons each consisting of 2, 3 or 4 individual systems. The structure of each battalion reflects the type of fire mission that any given system performs. For example tube artillery usually has 2 or 4 howitzers per fire platoon and 6 or 8 per battery.
The battery is the actual "fighting unit" of artillery battalions much like company is the actual fighting force of a combined arms battalion. Battalions don't fight and instead they deploy a battery to any single fire mission. The battery has 2 or 3 fire platoons which take turns shooting, relocating and reloading. Every fire platoon has a specific firepower that is calculated by number of shells per salvo and the number of salvoes to execute a fire mission.
The fire missions are traditionally described in artillery tables. The tables list how many shells of a given type are required to destroy, neutralize or suppress a given type of target.
If an artillery brigade has 6 battalions it means it has 12 to 18 batteries
managed by a single hq with a single recon/UAV unit.
It's a misconception that if a division consists of three brigades and each brigade has an artillery battalion then divisional artillery must have a battalion per brigade. Divisional artillery only fulfills roles that brigades can't. If the division is in combat then it usually fights with a single brigade forward i.e. with single artillery battalion forward. Divisional artillery doubles that number and there are potentially two more battalions from the two remaining brigades in the rear. If all three brigades are in active combat then they fight with reduced strength to rotate forces - a battalion forward with a battery supporting it, so again divisional artillery has sufficient forces to match.
A support unit only needs to fulfill the necessary tasks that the subordinate units can't fulfill. Once that is achieved it's more useful to pass the assets down the chain of command to lower echelon because they're more effectively used this way.
Concentration of assets is inefficient. It only is done when echelons are not competent to execute the tasks on their own.
So if this hypothetical artillery brigade has six battalions worth of assets it would make more sense to consolidate battalions and expand the batteries and fire platoons so the battalions are stronger and pass the remainder to other units. Or better yet it should be split into two arty brigades with three battalions each.
Also the typical structure is: 2 battalions of tube artillery and 1 battalion of rocket artillery or 1 battalion of short-range MLRS and 1 battalion of long-range MLRS if there are two types of systems in service. They're split due to logistics reqs, range and different artillery (damage) tables. The reason why there are two howitzer battalions is because they're slower (towed or tracked self-propelled) and are more easily reduced in effectiveness by losses due to enemy fire. So two battalions are used so that one is always ready for combat.
So to summarize this explanation:
If PLA uses 152/155mm howitzers, 122mm mlrs and 300mm mlrs it will have three battalions - one of each type - split into 2,3 or 4 batteries per requirement, and a "reserve" howitzer battalion to ensure availability of a single battalion.
For six battalions to make sense it would have to be two 122mm tube, two 152/155mm tube and single 122mm mlrs and 300mm mlrs but that doesn't make tactical sense because mixing 122mm tube and 152/155mm tube doesn't make tactical sense. 122mm is regimental artillery - it supports battalions, not brigades or divisions. The range of 15-20km puts it and its logistics too close to the front.
So it would have to be towed 152/155mm for air transport like US Army did in DivArty for divisions with SBCT/IBCT (25th) or ABCT/IBCT (4th). But that makes sense for a specific brigade supporting specific mix of units, not general structure.
In the past - per Soviet doctrine - artillery units had anti-tank artillery battalions and they're still part of Russian artillery groups in brigades but that is one more.
Ukrainian artillery brigades before the war also had 5 battalions each: 4x 152mm long range towed (2A36, 2A65) and 1x 100mm AT (MT-12) but they weren't proper artillery brigades but administrative units that aggregated artillery that would then support individual brigades (AFU brigades only had 2S3 and 2S1 so they were outranged by Russian 2S19) or individual battalions (because AFU brigades were often split into separate battalions fighting in different places). But that was bad planning and bad practice.
I expect PLA to be on Russian/US level of combined arms doctrine and those structures are publicly available online. Both concentrate tube artillery in large numbers but
within divisions. Separate arty brigades are small because that's the point.
So if you have a source please link it. Otherwise someone made a mistake and we shouldn't repeat it.