[Christian]

My forecast view is cluttered with daily routine stuff that obscures my less-routine actions.

Trying to understand the issue here. If these tasks have to be done on, say, Friday then I need a measure to see that I have to do them that day. It does not matter if the task is "clean gutter" or "clean nuclear power plant". I have to do it and I need to be reminded of doing it. How does it clutter the view just because it is a regular task? If you do not need to be reminded, don't put it in OF. If you need to be reminded, it is not in the way.

I've spent so much time in the forecast that I've gotten in the habit of "living" there instead of switching among contexts throughout the day.

Forecast shows all tasks that you have to finish today. As long as you get them done, staying there is nothing bad. No need to cycle through the contexts if you can still do the things you have to. On the contrary, staying in forecast until you have those things checked off means that the time critical stuff is done before you do other things, going by contexts.

My iPhone slows with a few hundred checked-off actions before I archive them each month.

Make a new task to archive your old actions once every two weeks. It only takes a minute.