I don't want it to be one-sided. Light-hearted whimsy is ideal in a Zelda game because it's better for absorbing all the experiences you have exploring Hyrule (or Termina or Koholint or Holodrum or whatevertheheck) in a memorable, positive way. But too much light-heartedness will make the game stale, and it will get in the way of experiencing serious, emotional moments. Likewise, too much darkness becomes stale and corny, and after a while you'd just be rolling your eyes.
There needs to be a balance. Serious moments like witnessing a couple deciding to spend their last moments together. Joyful moments like waking the person closest to you from their thousand-year slumber. Having chills down your spine while creeping around a torture chamber hidden away underground or within a hidden temple. Soaring freely through the air at top speeds and exploring remnants of an old, forgotten temple.
A Zelda game that is just dark (TP) or just light-hearted (PH/ST/(SS?) ) never feels completely satisfying. In fact, I think the only two that have really been either very dark or very light-hearted and have been very enjoyable were Majora's Mask and Link's Awakening, and I think the only reason they were able to do it was because they were both incredibly unique to a series that was already unique as a whole. I think it's rare, and I'd rather see a wonderful mix of the two than a failed attempt at trying to recreate their mostly-dark or morely-light-hearted successes.