Hopdoc
You are correct.

No matter how strong the steel is, a big calibre double needs a certain amount of weight to be "shootable".

My 450/400 weighs about 10 lbs 2 oz with its Murray leather shell carrier on the stock, but with no shells in it.

My 450 No2 has 28" bbls and weighs about 11 3/4 lbs with its shell carrier.
both rifles balance perfectly are comfortable to shoot and do not feel too heavy.

I have carried them many a mile.

Modern steel has enabled smaller calibre doubles to be made lighter. My 9,3x74R Chapuis weighs 7 1/4 lbs, early 303 doubles weighed 10 lbs or more.

The lightest sleekest of the new made doubles is the new Merkel on the 28ga frame with the 21" bbls. I have handled and shot one in 9,3x74R several rounds. I like it.

Since I have a 9,3 double and a 9,3 double rifle drilling, I would love to have one of the new Merkels in 308 WCF [as I have a lot of ammo for it], but for everyone else the 9,3x74R is a better calibre.