i believe if the current trend goes on, you'll soon likely have not much on your local machine anymore that would be worth protecting. The philosophy behind devices like the Cromebook or streaming apps like photoshop-in-the-cloud after all only work if all your files are also in the cloud. So if this catches on, expect your Dropbox/Google Drive/etc to turn from a convenient place to backup and move your files to the primary location where you store them.
Even if you have valuable files stored locally, you'd be correct if access to cloud services would really only run through the browser. but check how all recent Android or iOS releases (or really almost all modern consumer OSes) work: most regularly phone home to their respective vendor and are usually heavily locked down - the devices are little more than physical endpoints if the cloud. On such devices, the company that created the device has likely mider access to the system than you.
obviously there are the usual exceptions from the Free Software movement - however for average consumer devices, the trend seems to be clear.
Although honestly, for something like photoshop I really don't see a problem. It's a creative tool, and probably isn't producing interesting data for the NSA, et al. The real security concern here is Adobe's, in that they want to protect their software from you, the user. They want to set up an annuity-style revenue stream, and the only way to do that is to protect the binary image of their software. So they did that.
Really, the only objection I would have to this is that it adds a (sometimes rather difficult to meet) requirement that you have a solid internet connection to run what used to be a stand-alone application. More philosophically, I object to the horrible waste this kind of runtime requires, particularly of network bandwidth. Perhaps, though, this is the price of saving the premium proprietary software market.
Perhaps for non-technical users. For technical users this is a solved problem for a few decades now. You can restrict read/write access for any software in any which way you want.
>Running in a virtualized environment in a browser significantly reduces access to your system.
Why would I want to kill my software performance by running it on an inferior browser platform when the kernel is perfectly capable of compartmentalizing software.