I think you're overstating it. Titan has encountered Picard in exactly one of the 11 novels it has appeared in - the third Destiny novel (and maybe a tiny bit right at the end of 2). And a lot of the other books have been concerned with major political movements where you'd expect the Federation flagship to be engaged.
If anything, it's a lot more IMplausible that the Ent-E wouldn't have ever appeared in any of the Dominion War battles on DS9. The only reason that they didn't cross over MORE was budgetary constraints.