Big fan of Kupp's, and would 100% agree he's not a system WR, he'd be good almost anywhere, but the most important WR is easily Cooks. He's the guy keeping safeties deep, he's the guy causing Gurley to see 6-man boxes, even though he's on pace to set the NFL TD record, and he's the guy clearing out for Kupp and Woods to get favorable matchups underneath. He's arguably the 2nd most important player on the offense(after Goff, and ahead of Gurley) and he's been worth both the 1st round pick(all 3 that he has been acquired with in his career) and the big contract. Both the Saints and Patriots have have missed his presence, and to their credit, due to having excellent QB/HC's adjusted their offenses accordingly, almost any other teams would have been crippled trying to replace a guy like Cooks, who i believe is a top-10 NFL WR, even if that doesn't always show up fantasy wise.
All that said, I think Goff would still have success minus any of these guys. He and McVay are on a wavelength that few QB's and HC's ever get on. That alone makes Goff a QB1 fantasy wise, but with the level of weapons he has, he's a threat for QB1 overall with even a minor tweak in redzone playcalling. Its very telling that even when inside the 10, teams still play 6-man boxes against Gurley because they are more afraid of Goff.
I'm a little off topic as to the post I'm replying to here, but I think Goff is a huge buy low guy in dynasty right now. He's not cheap, but getting him now, might be like getting Brees in 2006, when people mistakenly thought he was playing at his ceiling. What Goff is doing right now, feels a lot like his floor, and its still a quality QB1.