I like how I can create a workout template and use it for several clients, but once I add that workout to their calendar, I can't swap individual exercises for substitution exercises or add scaling options for clients with bad knees, shoulders, etc...

For this, the only option I see is to add a whole new template just for one client rather than have them follow a similar routine where I can delete and exchange "weighted dips" for "machine assisted dips", for example, while they recover from a work-related injury.

If I get to the point where I have 50-60 clients, you can see how time-consuming it would be to create scaling options for 30 clients on a 12-week plan.