What we lose with a time jump: talented young actors that we will be attached to by the end of season 1.
What we gain: being closer to making the show about Batman instead of Jim Gordon, the main character.
I know some people really want this show to be a Batman series, but... it's just not. Yes, if they wanted, season 2 (or 3) could be about Batman teaming up with Jim Gordon and they could share the show, but is it possible, just possible, that not only is that not the intent of the show, but that the show is better because it's not that. Because this isn't a superhero show, the bad guys don't have to lose hardly ever, and that alone makes this show much more interesting than a low-rent Batman (compared to the version coming out in a couple years).
Having a GCPD Show where Batman drops in is like having a Robin show with Batman as a supporting character. It could be okay, but everyone is always going to want more Batman because he's the more popular character. I mean think about it, Batman is just a kid and people are already calling for time jumps to put more focus on Batman. Imagine of Batman were just around... who would want to see Jim Gordon's inferior detective work, combat abilities and social presence? The thread wouldn't be 'will we ever see Batman' it would be 'when will the series finally focus on Batman?'
Let's just enjoy the show that they've developed and pitched and has gotten critical and commercial acclaim, one where the last shot is David Mazouz putting on the cowl. Not as a means to an end, but as an end in itself, the end of the era of a hopelessly corrupt Gotham and the beginning of the era of Batman.