Follow-up: can we switch themes w/o `setOptions` for charts

[akashsonune]

can we switch themes w/o setOptions for both charts? This of course also mean no applyPalette, etc. above which will probably break some of our own charts.

Let's keep it for now but keep it in mind. This MR is a huge improvement already as-is! 💯

Originally posted by @dr-itz in #567 (comment)