The real question to be asked is "Are 5 stars still worth ranking up?" Say you have your favourite champion as a 5-star but is it worth ranking them up if they won't do well against the content you're facing? 6 star rank threes have become so common that 6* R2s and 5* R5s are (imo) pretty much obsolete now except for niche rank-ups like Herc (no-brainer), Magneto (shuts down metal completely) and Human Torch (for mystics)
Now that 7* are out and people are raving, is ranking up 6* a waste of time?