My mental sanity depends on some fixed beliefs. One of those is that every key sequence not involving the Win key is sent to and handled by the application in focus. Including F-keys, which many applications expect, in any case. Ex: F2=edit cell, F9=recalculate in Excel.
Global actions handled by the SO or DE must involve Win. Ex: Win+L lock screen.
And yes, Redmond-imposed Alt-Tab is an abomination: it should have been Win+Tab since the beginning.
The workflow you're proposing could be easily achieved with Win+ a carefully chosen letter. Benefits: 1. the letter is easier to remember; 2. You have 20-something free slots instead of 12 (excluding the ones that are already taken for standard actions like L for lock); 3. Most probably your fingers are already there and you have muscles memory of where the letters are; 4. Consistent, expected behavior of where keys are sent to.