I don't want to change the offense either, trust me. And I'm OK with tagging him. Just saying there are valid arguments either way. You can spin it a lot of different ways. For example if they tag him they can say "look, we paid him $700k last year so we see it as paying him $16.7M for two years." Also, Watkins' 5th year option for 2018 that the Bills declined would have been $13.3M. So the Rams can also say "we're paying a little more for his 5th year without having drafted him."
I do think he makes players around him better and helps the whole offense 'go.' Either way I don't expect some massive spike in his production but I would much rather him be a Ram in 2018 than not. I don't think tagging him precludes them from getting Donald's deal done, keeping Joyner, extending Robey-Coleman and Sullivan, etc. The trade-off for being protected against a bad long-term deal is paying more short term. Like I said in another post it's what should have happened with Austin.