"(...) so there's something slightly awkward in a Mario with a restricted moveset being pushed towards a very different style of play (and something slightly disappointing in how Bowser's Fury alone only manages 30fps when playing in handheld - a tribute to Sunshine too far, I feel, though it's understandable given the scale of the open world undertaking)".
So, to highlight the update the author made, Super Mario 3D World runs at 60 fps in both docked and portable modes, whereas Bowser's Fury runs at 60 fps only docked, handheld gameplay is limited to 30. Obviously, the different and open approach of this expansion pushes the Switch harder, and so the developers decided to cap the frame rate at 30. There could be more games that go through the same situation, but the only other example I know of is DOOM Eternal, the cutscenes in this game run at 30 fps in docked mode, but in portable they run at 20. So, in essence, these discrepancies become more common going forward. Another sign that the rumored Pro model could be a sizeable upgrade?