It's open for debate, sure, but I'd include them. The arbitrary definition 'Test standard' is one reason why. Think it goes without saying that a few FC sides (NSW, for example) would have had higher standard of play than some international teams, definitely Zim/Bangladesh and at various times WI and Pakistan. If you're going to omit them, why not include runs scored/wickets taken against FC teams like that? They're not playing in Tests because Tests are between countries (an arbitrary distinction for many strong FC teams) but runs scored/wickets taken against them, if played at an agreed-upon 'Test standard', should be counted if we're going to discount Zim/Bang for their standard of play, no?
tbh, dealing with this in data analysis is actually pretty straightforward. If you're going to insist on using the virtually worthless measures of 'runs scored' and 'wickets taken' without sampling, just weight different teams at different times differently. Come up with a multiplier for different teams and/or at different times in their history and apply it to any game any player plays against them. 250 runs against Bangladesh for Jan 2003 becomes worth less than 250 runs against England the next month. Easy. If you take a sample, it becomes even easier.
Of course, this is predicated on the assumption that any player doesn't improve or decline. Yikes @ taking that into account .