While this is true, keep in mind that the system is smart enough to know the role you're actually playing, and doesn't just go by the role you were assigned.
So if you want to go blitz adc with a vayne support, then sure it would require relatively 'meh' scores to get S+'s, but vayne support is probably going to be pretty lame (blitz adc is technically a thing). If blitz 'adc' and vayne 'support' involves vayne csing and blitz building a support item instead of vice versa, then the vayne will be compared to vayne adc's even if they queued as support, and the blitz compared to blitz supports.
As such if I was trying to get an 'easy' S grade by playing off-meta stuff, I'd play whatever off-meta adc, and hope that I had an exceptionally talented meta support to actually support properly and ideally spoon feed the kills to me and/or keep me alive. (Alternatively, I'd want a top tier adc as I played an extremely off meta support, who could basically carry themselves and I'd be there to 'help' leech assists while probably not actually being that effective.)
edit: And for what it's worth I suspect lucian might possibly be one of the worst possible supports. Everyone one of his abilities is damage focused and doesn't offer any utility. Vayne support could at least be 'supporty' by condeming someone into a wall or away from the carry.