I agree, if stats aren't a concern Palkia is the beginning and the end, smashing through walls is too convenient to pass up. But with an average amount of investment (lv100 and max IQ through gummy spam, no trap protection), I'd rather pick a female Drifloon with a moveset of Ominous Wind/Silver Wind/Stockpile/Shadow Ball.

Drifloon's "fatal" flaw is that it can't carve its way through walls like Palkia. Leaving that aside, it still has Map Surveyor + Stairs Sensor to slice through dungeons, and unlike Palkia it gets Trap Seer to eliminate any trap-related concerns. All in all, still an excellent option on that front, but Palkia is just broken.

On the matter of combat, however, the advantage is firmly with the little balloon that could. Unburden is definitely a big asset, but the more important thing is how well everything else complenents it.
Quick Striker lets Drifloon do a guaranteed four (4) standard attacks in a turn, which allows to take on most isolated enemies without any PP usage at all, especially since a single use of Stockpile allows Drifloon to just tank hits all day long thanks to Unburden doubling it up.
If the enemy isn't isolated, then a single (double thanks to Unburden) Ominous or Silver Wind will most likely either mow down the opposition or give Drifloon a speed boost to fight or possibly flee instead. On the other hand, Palkia's definitely got some strong attacks but if it can't one-shot its opposition it can be easily overwhelmed like anything else.