"Fearful of the Klingons?" How so? They were shown throughout early TNG to be stalwart allies.
Just watch "Heart of Glory" or "A Matter of Honor". Essentially, Klingons are more alien to our heroes than the potential joint offspring of Crystalline Entity and Nagilum, and their friendliest form of cooperation is "We're not going to fire at you today... If all goes well". "Aquiel" establishes that these "allies" kept raiding Federation installations right until the beginning of TNG. And apparently no Starfleet officer has served on a Klingon vessel or installation before "A Matter of Honor", even though TNG shows many Klingons working for the Federation in various roles. Essentially, everybody but Riker is trembling in their pants or skants during the early seasons, and Riker probably only gets through "A Matter of Honor" by grinding his teeth - against a Diapam pill.
It would have been near-impossible for Picard to form a close rapport with these "allies" before TNG, IMHO.
Me, too. Retroactively insert a smiley if needed...
Still, perhaps Picard was consciously trying to avoid the stereotype of a babbling old man when he failed to bring up his past experiences at every turn? And it's not as if Kirk ever explicitly mentioned his previous dealings with the Klingons in "Errand of Mercy", or returned to those in any later episode, either. Being familiar with a recurring villain species would be a bit different from being familiar with the alien planet of the week, and wouldn't necessarily warrant a mention.