I'd rather the VG than the Star Anvil. It's not particularly efficient at anything but engaging super heavy war engines, and not even well suited to fighting other Eldar super heavies. If we want armor support we'd probably be better off with a handful of grav tanks rather than a singular super heavy suited for hunting Gargants and Warhounds.
Outside of fighting other Eldar we're basically always going to be massively outnumbered. Dispersion and volume of fire is the best way to counter the Holo-Field and Grav-Shield combo and the Orks have both in spades.
Mass artillery fire is actually pretty good IRL Vs armor as even if the thickest parts of your tanks are well armored enough to shrug off anything that isn't a direct hit the lightly or unarmored bits of your tank where some critical components are can't (I highly doubt all the important bits of our tank are fully underarmor as you kinda need your sensors to to be exposed to be able to see things for example).
Our mortars likely won't be outranging much unless we go for the superheavy ones given the description from the Seeker entry explicitly calls them short ranged so we aren't going to have that much downtime before counterbattery fire starts up.
You're just ignoring the time it takes to bring so many artillery pieces to bear, or the utter difficulty of Orks coordinating a battery, let alone communicating the accurate location of a suspected artillery piece to be counter-batteried. Counter battery has never,
and will never be the province of a hundred guns individually shooting at something they individually think should explode. You're handwaving the need for a battery to be incredibly quickly given accurate coordinates based off really quick deductions. With no communication errors, no personalities butting head, etc.
Ork artillery is probably pretty alright in a direct fire role, decent at suppressing a location or shelling fortifications- but the idea that their artillery is so responsive and so well coordinated they can engage hostile SPGs that
can fire on the move* with enough reliability so as to easily counter it? I'm skeptical to say the least.
*Crystal Targeting Matrixes are a thing.
The question isn't, Light SPG Skimmer with a fusion mortar OR Grav-tank with Vehicle fusion mortars OR a Heavy Grav Tank with Dual superheavy Mortars. The Answer is that I want all three of those, So the question is when can we afford the actions to develope all of them.
Yeah, all of these serve slightly different roles and are all useful capabilities in their own right. A skimmer is a lot easier to have organically in a line detachment than a grav tank artillery vehicle or a super heavy artillery vehicle but those are going to have more firepower and staying power.
I favor developing the lighter organic artillery and support roles before we develop the more specialized heavier vehicles just because it gives us a bit more room to decide how many of the latter we want now that a baseline has been established.
You are also being incredibly optimistic assuming we can just pick off any hostile seers with Fatecasters since that is the sort of thing they should be able to forsee and if they're buttoned up inside a armored vehicle (y'know like ours are in our Mech HQ detachments) you're going to need something heavier than Fatecasters Rifles to tag them.
It's the sort of thing they need to actively be looking for and countering the entire time, especially given seers right now are in their infancy and as weak in their powers as they will ever be. If they're buttoned up in an APC they're not really helping their own situation all that much either given our anti-armor weaponry is going to be significantly better as a matter of course. To say nothing of the fact a Fatecaster is not some small caliber rifle. It's the bigger and mean version of a Shuriken Cannon and whatever vehicle the Seer is trying to hide it- it's not going to be a Wave Serpent or a Falcon just yet.
The idea their seers can casually direct counter batteries with artillery Biel-Tan shouldn't have yet (and most Craftworld artillery are monofilaments that would be awful for fighting a vehicle with) while completely hidden and with no retaliation from our High Technology snipers, Anti-Armor specialists, or Seers of our own is just presuming the enemy has total freedom to act and react as they choose.
I can't even call you pessimistic, your arguments just seem contingent on the assumption that our artillery has to fight the entire enemy army on their lonesome.
