siemian looked competent in 4 games this year - in all the rest he looked like the worst qb in football and thomas has had qb play of the lowest quality for most of this year (the first 3 games aside)...
and great wrs dont make plays whoever is playing qb - even antonio brown disappears sometimes when big ben isnt the qb... mike evans, aj green, ty hilton, dez bryant etc. all suffer when they dont have good qb play servicing them
the only wr in the league who consistently plays well no matter what level of qb play he gets is Deandre Hopkins...