Yeah, it gets really annoying having overworld background music constantly being interrupted by the same old music theme that in no way blends or matches the ambiance or atmosphere of your current surroundings. Imagine, walking through a dank, dark cavern with ominous music in the background then... UPBEAT BATTLE THEME!
I wonder why JRPG designers haven't put much thought into developing more dynamic music that takes into account of the current overworld and has an appropriate predefined battle track that can seamlessly be played after the overworld track stops. Then it won't seem like you're listening to a different and disjointed track.