Question about Rollups (how effectively do they really scale Ethereum?)

Hi,

I'm just reading that Rollups are supposed to be out in about 1 month according to Vitalik and that it scales transaction capacity about 100x (so presumably if applied to the entire network at once the fees can go down 100 fold).Â

However, as it is a layer 2 solution, I gather each project/protocol has to implement it individually. Therefore, does that mean that if a project implements it fully the fees for transacting in their token still don't go down 100 fold? The other projects haven't won't have transitioned yet, so are still clogging up the Ethereum network. So for example, if Synthetix implements rollups, then fees for transacting in SNX and their other synthetic derivatives will not reduce by 100 fold, or anything near, because all the other Ethereum projects also need to implement it, so maybe the fees go down in proportion to how numerous the SNX and their synthetic token transactions are on the Ethereum network, which is no where near 100%. In which case each project is actually incentivised to do nothing and wait for someone else to implement it first and reduce their transaction costs for them (a tragedy of the commons problem).

Is this a valid issue? Also, what about ETH-only transactions? (as in just transacting ETH – not a token/layer 2 – I am presuming this is what is meant by layer 2, i.e. a token). Do all ETH all automatically scale with rollups and therefore go down partially in cost (with all the other transactions in tokens still clogging it up and so costs are still high but partially reduced in proportion to the number of ETH-only transactions?).

Thank you