The Executioner is much more reliable if you use Long Barrel and ADS for each shot. With long barrel, Executioner is comparable to an unmodified S12, only slightly inferior.
The crossbow is underwhelming for sure. Still, with 6 shots, its still useful for exploding vehicle kills and for killing anyone using a shield. Also, tri-bolt helps tremendously.
While it might be neat to see, perk based model details don't seem like they would be appreciated in a game like this. Exposure time to enemies is very low in CoD (depending on platform and player, as low as 1/5 second). Being able to determine what someone is carrying beyond his/her primary weapon provides little to no advantage.
Concerning black hat: I don't think it would be fair to allow sentry guns and guardians to be stolen that easily just because someone happens to have the right perk (that allows them to see them anywhere on the map). If you don't like having them destroyed, imagine how irritating it is to have your streaks stolen every time you drop them.
"Having to earn that score streak and then detroyed the moment its set up really bites."