Batista was barely even over until late 2004. I remember a guy amusingly holding up a sign at Survivor Series 2004 that read, "Hahaha, Batista can't get over." It was only when they started teasing around December him turning on Triple H and breaking away from Evolution that he started getting massive cheers week after week. And by the time the Rumble and Wrestlemania arrived, Batista was over like rover and HHH putting him over clean three PPVs in a row made him into a bonafide main event superstar. Reigns has actually been over as a singles competitor for a longer stretch of time than Batista was before he was pushed to the moon, so it's not hard to see why WWE were confident that the fan-base would accept Reigns as the next guy. One of the issues was that if Bryan wasn't gonna win the Rumble, then he shouldn't have even been in it. And since he was only officially cleared to wrestle a month ago, they could have easily held off his return until after the Rumble, and then a rowdy crowd like Philadelphia (ironic that it's called "The City Of Brotherly Love" lol) wouldn't get their hopes up for Bryan winning it in the first place.
The problem with your comparison is that Batista was in a different situation than Roman Reigns was in. Batista was a member of Evolution and had a lot of personal business with Triple H. The whole Evolution and Randy Orton dismissal from Evolution was one of the strongest stories of the year. So when Batista turned on Triple H and Ric Flair, it made sense for the fans to cheer him because of his personal connection to Evolution. WWE was teasing a Batista turn on Triple H for at least two months before the turn happened. Batista got over not simply because he was Batista but because he was a person with a personal connection with Triple H and the feud made sense. If Batista had done what Triple H had suggested and gone to Smackdown to face JBL, I have no doubt the fans would not have warmed up to him in the same way. I do realize, however, that is complete speculation.
In reference to Reigns, I have said over and over that if Seth Rollins was champion and Reigns won the Royal Rumble, then the match makes sense. The fan base would be behind that and likely would generate a lot of support for Reigns. Against Lesnar,with whom Reigns has had zero interaction, it just doesn't make sense.
The reason it is different Bryan and Lesnar than Reigns and Lesnar is that Bryan is already remarkably over. He doesn't need any connections with his opponents to get over. You put Daniel Bryan up against a cardboard box at this point and the fans will be behind him.
I didn't like the idea of Reigns winning, but now that he has and WWE has to stick with it. They can't pull another triple threat or anything like they did last year. Daniel Bryan just isn't going to be in the main event unless he somehow gets the belt in a match before then, which is unlikely.