You will need a sub-second network speed, in some cases < X ms, if you want to offer an acceptable UX for "heavy user interaction" software, like the photo editor you mentioned.
Even the cloud won't save you, though: some SaaS companies are far too easy to replicate internally. It kind of sucks, because these used to be small companies with a couple of use cases in mind that nobody ever wanted to "reimplement internally" and they did give work to real people. But now, throw some agents at it, and a few 100s $ later you have replicated their product and can run it in your (internal) network.
Even the cloud won't save you, though: some SaaS companies are far too easy to replicate internally. It kind of sucks, because these used to be small companies with a couple of use cases in mind that nobody ever wanted to "reimplement internally" and they did give work to real people. But now, throw some agents at it, and a few 100s $ later you have replicated their product and can run it in your (internal) network.