I don't know what the passing game snap rates are (maybe someone has them) but based off what they seem to be watching the two players it appears (and I say this knowing how wrong I could be) that Booker's on the field a lot more in passing situations than Ajayi is. It appears to me watching Denver and Miami games that Williams is on the field a lot more than Bibbs in passing situations. Booker isn't getting a lot of receptions as the starter but he seems to be on the field a lot on passing situations whereas it appears to me when watching Miami games that Ajayi tends to come out a lot in those situations. Again, I could be completely mistaken about that since I'm just going off memory here.
But I will say Booker is definitely the superior receiver watching the two players. I'm not sure there would much disagreement about that among scouts or GMs. He looks to be far more natural in the passing game and I'm surprised Kubiak isn't using him a lot more consistently since Anderson went down. His role in the passing game seems to have regressed since he became the starter which is rather odd.
I think Jay Ajayi has regressed somewhat as a receiver which is kind of strange to me, but that does seem to be the case at least for now. Damien Williams has morphed into a RB/FB role as he is really good at blocking and Miami had TE's injured, Williams has always been a pretty good receiving option too. Jay has had drops and things to cause Gase to perhaps not trust him to be involved more as a receiver than he has.
I agree with you that Booker had worked his way into a receiving RB role as COP to Anderson and I think he was getting more targets in the passing game then. Now with Anderson injured, he has more of a traditional role and not as many targets.
The speculation about Lynch possibly checking down to RB more than Siemien is an interesting angle to consider, as it could play out that way and that would benefit Booker for this game in terms of more targets.
It is always possible Gase changes things and tries to throw to Jay more against the Ravens, I don't feel like I can count on the game script and coaching changes that there isn't enough evidence to support.
The one game that Lynch played isn't enough of a sample for such a projection in my opinion, but if he does target RB more than Siemien has, it is something we can compare as far as differences in tendencies. Two games of Lynch a lot better sample than one.
In the first game Lynch played against Tampa (Simien injured) he threw to Fowler 3 times, Anderson once, Booker once. So 5 target to the RB.
Against the Falcons 6 targets for Booker, 4 for Anderson and 2 for Fowler. 12 targets to the RB.
The average number of targets to RB based off of this would be 8.5 which will likely be split between Booker and Bibbs. This still seems a bit too optimistic and skewed by the results of the Falcons game. A 3rd game would be something I would feel more comfortable with as far as how Lynch distributes the football to players.
I think the high targets against Atlanta had to do with the Falcon's having some good corners (unlike Tampa) and therefore an easier match up to throw to the RB more.