Feel free to "fall in love" with this guy, but if you don't read about him getting first team reps next summer you have to strongly consider bailing.
I think you make some good points here, particularly with getting reps (or the lack thereof) being tied to success in the NFL. Also I agree that a first round choice will be given every opportunity to make it, while less patience is given to those taken in later rounds - almost with a direct correlation to where a player was drafted (some organizations like The Saints being an exception).However, I don't believe that a first round pick would necessarily be the kiss-of-death for DX with the Rams. Your examples are interesting, but Dez Bryant was drafted because of how disappointing Roy Williams has been for the Cowboys - so it is hardly surprising he was given a shot at starting over him. Yes, the Titans have been very patient with Britt, but what serious competion has he had? Same with Crabtree, a super talent who started two weeks after coming in, but he only had to beat out Isaac Bruce, Josh Morgan and Jason Hill.
Anyway, I think the people that like DX here are just recommending him as a sleeper pick that you can acquire fairly cheaply - not suggesting you mortgage the farm to get him. Yes, if Clayton comes back he may be 3rd string. If a free agent like Vincent Jackson is brought in, then he doesn't have much value at all. A first round WR would certainly throw a monkey wrench into his prospects but considering about 40-50% of those are complete busts, it might still work out for him.
This is simply a player with high upside to take a flyer on. Will he ultimately succeed? Probably not - but I think he is worth trying to acquire with his asking price currently being devalued due to his injury history and all the uncertainty as to how the WR position will shake out with the Rams next year.