Yes, I think you are on the right lines here. I am just finishing up my first game against the AI at the default Veteran level with the new patch and the basic narrative still is - "artillery has won the war". I am playing as the Central Powers and I am getting blasted out of my positions on the Western Front by a line of British and French guns. The game is well into the summer of 1918 and the USA has not joined the war yet. I have defeated Russia, Serbia, Albania and driven the British out of Iraq.
So my first impression is that although the changes to artillery in the new patch are welcome, they do not alter the basic dynamic of the game too much. In another thread I have suggested one possible way of tweaking artillery fire in relation to the heavier fortifications in the game. Of course, there are different ways of going at this.
I am a bit confused about what the Artillery units in the game actually represent, other than that they are "concentrations" of artillery. Given that Infantry units can sink dreadnoughts that are in a port, presumably because they have smaller field guns with them (and presumably Cavalry Corps units have horse artillery detachments included with them as well), then these Artillery units can only represent the heavier type guns. But where is the dividing line? I need to do some research to identify the main types of larger gun, but would the UK have 4 larger guns (however defined) when France only has 3? Would the UK have deployed them all in France, or 3 in France and 1 in Egypt?
I see in the Editor that there are 3 types of Artillery - Artillery, Heavy Artillery and Super Heavy Artillery - but only Artillery is activated, which suggests to me that the Artillery units in the game probably include middle range guns and howitzers and Infantry units just have the smaller field guns. But how effective were these middle-sized guns against fortified positions? At the moment, particularly in the later game from 1916 onwards, it feels like Super Heavy Artillery fire is being used everywhere and is the dominant type of artillery fire.
On the evidence of this first play through with the new patch I think I will go back to my very basic mod that has a 6 artillery shells maximum instead of 10.
Considering the scale of the game I think the most accurate description would be the concentration of artillery including stockpiling of ammunition and high level of planning/coordination.
The typical Corps sized infantry force that occupies a single square in SC:WW1 would have both light and heavy artillery with it. No "hex" would be manned just by infantry and light artillery without any heavy artillery, air elements or cavalry. Units like Detachments and Garrisons are relatively weak on offense and I assume that is because they have relatively small amount of artillery compared to Corps sized units.
As a historical example, at battle of St. Quentin Canal in September 1918 the Entente forces started an assault on German line with "56 hour" artillery bombardment. The British has amassed over 1600 artillery pieces (1,044 field guns and 593 heavy guns and howitzers) for a 10.000 yard long front, which fired almost a million shells during the last 24 hours of the bombardment. That heavy gun concentration is still not even close to the total amount of guns the British had, but the number of involved guns, the prepared stockpile of ammunition, and the degree on preliminary planning was obviously well beyond the normal level.
The advancement in artillery technology and doctrine at St. Question was also obvious. At the start of the war in 1914 the artillery was largely light direct fire support with the larger "siege" guns rare and underdeveloped. The artillery shell consumption had been severely underestimated resulting to stuff like the 1915 Shell Crisis.
At battle of Somme in 1916 the massive Entente artillery bombardment of over 1,6 million shells failed to destroy the German fortification (apparently they used shrapnel shells among other mistakes). The tech and doctrine had improved significantly but were far from perfect.
However at St. Quentin the well planned bombardment included special fuses for destroying the barbed wire, gas shells for hitting the enemy artillery, supply and HQ units, as well as creeping barrages to support the infantry assault. All that allowed the Entente to break through the Hindenburg line with relative ease. I think it's safe to say that in the end it was the artillery that won the battle and the war (on the battlefields at least).
This kind of well prepared large artillery operation is what I assume the in-game artillery "unit" represents, rather than just a literal collection on guns. With slowed down development of artillery in the latest patch of SC:WW1 the pace of artillery development seems to better match the historical course, although the research of ammo production could be still be slower for it to be maxed closer to the end of war.
The maximum amount of ammo per artillery unit could be slightly lower because two artillery units can still neuter any fortification in the game from full strength in a single turn without any input from the defender before the attacker can take over with minimal losses. At St. Quentin Canal it doesn't seem like the Entente had any massive advantage in the numbers of infantry but they still won (which is pretty remarkable considering the losses the attacker would typically suffered just couple years earlier). Even though they won, they still suffered about 24,000 casualties to the Germany's 36,000. That is far more relative casualties than you will typically suffer taking a hex after a (fully upgraded) artillery preparation in-game.
If I have understood correctly, the different types of artillery units in SC:WW1 exist for use in smaller scale scenarios where differentiating between artillery types actually makes sense (i.e. "Move this heavy artillery brigade from this village to that field"). On strategic scale you are not really going to say "Lets send all the 155mm guns to Somme and leave nothing but 75mm to the rest of the front". At strategic level the artillery will move and operate as a part of larger formations and at most you will have a relatively high concentration of well prepared and organized heavy artillery at specific part of the the front, rather than permanently independent massive artillery formations with exclusively big guns moving around freely.