If there isn't truly any separation for witness data and non-witness data, then does that mean that making the block size larger, let's make "triple" the current size, won't truly help the network if the demand for block space increases as well?
Exactly.
1. If you want to increase maximum block size from 4 MB witness into 12 MB "second witness", then you need another soft-fork, if you want to have that data processed, and stored by every single full node (because if not, then it is easy, and you can have "unlimited commitments", that would be recognized only by upgraded nodes, and nobody else).
2. If you would have for example 12 MB "second witness", then each block would still have "1 MB legacy" limit, which means, if you can consume M UTXOs, and create N UTXOs on average, within a 4 MB witness, then that value will not increase in case of 12 MB "second witness", or even 1 GB "second witness", because all UTXOs are consumed and created in a "1 MB legacy" section, which means, that all non-Segwit nodes, still need to get that information in a backward-compatible way.
What it might actually do is encourage more developers to inscribe and mint BRC-20 tokens and NFTs.
If someone really want that functionality, then it is better to use commitments, than to push those data on-chain. Which means, if you have any signature, then you can convert R-value of that, into a matching Taproot address, and then upgraded nodes can store commitments to that data. Then, it is cheaper, and it is enforced by consensus rules in the same way, because Ordinals are just huge OP_NOPs, which means, you only need a matching connection between your data, and a particular address. And you don't need to push that data on-chain, to reach such connection. And also, moving things from TapScript into "any signature" means, that people could use those features on all address types, where OP_CHECKSIG is available, including altcoins like Grin.
Because, there are some users that are suggesting that they want a block size increase under the display of "It's merely a joke, bro".
I guess many people didn't try to change witness factor from 4 into 12 or anything bigger, and check, what is the final outcome of changes like that. Because I guess they think about it as "1 MB legacy + 3 MB witness", but this is not the case.
Edit: Also, in case of commitments, it is really "4 MB witness + unlimited commitments", which is what some people want, so I don't understand, why they don't want to implement it in that way, and they want block size increase instead.