In my opinion the Society would be more likely to invest in SH vehicles, although that would require more development time than they historically got time for...
They probably would although I don't know about taking more time to develop.
Because there's this thing called making an apples to apples comparison. Obviously, 1 40 ton Mech will beat 1 20 ton Mech. That's not a meaningful comparison.
Now 1 40 vs 2 20s, yeah that's going to be a much more even fight.
Not necessarily. A Locust with the same weapons vs Cicada 2A is even money. Actually, just swapping the MGs for 2 SLs and a 2nd ML would give the Locust more firepower than the Cicada.
You want to fight evenly?

Then you're looking at the numbers wrong. Those 2 super heavies would be massively more expensive, and no faster than a lance of vehicles moving the same volume of artillery around. It's mathematically impossible for Super Heavies to be a superior choice.
I agree. Superheavies would be massively expensive. However, considering the prices of some parts on mechs being mass produced in the IS, even the Periphery could be producing Superheavies and LAMs. So cost is only a factor if you want to go there.
When did I say Superior?

Although they might be transportation wise if you consider how heavy Bays could be. Even at 400 tons for a Superheavy Mech Bay two would be 800 tons. That'd be 400 less than that of 12 HV Bays. And I think 400 tons is probably 100 tons too much. So you could possibly carry 1 lance of superheavy mechs to a company of vehicles. That'd reduce the cost of food and such. Not that I'd plan to do that for every assault. They're Specialists. You'd bring them when assaulting a really hardened target.
How do you get a company of artillery in a superheavy? A company is 12 vees, and the most arty you can get in a superheavy is, as near as I can tell, 5.
If you're using the real world definition maybe.
A 200 ton Superheavy with 20 ton ES IS, a 52.5 400 Engine, 8 ton Gyro, 4 ton Cockpit, 10 extra clan DHS and 19.5 tons of armor takes 114 tons. That leaves plenty of tonnage for 6 artillery pieces.