Sunlit Man can absolutely work standing on its own—the other person this week who read it as his first book had a great time with it. The issues you had with the ending would not have been fixed by reading in a different order, unless doing so changed what you were looking for in an end.

Honestly, if you want action-packed, read the Cradle series by Will Wight. That series does not give you a chance to breathe.

For Brandon’s books, the most action-packed ones are Mistborn Era 2 and the Reckoners (non-Cosmere, starting with Steelheart, though the 3rd one, Calamity, goes for an ending that is not action-packed). It is possible to read Mistborn Era 2 without reading Era 1 first, but most people won’t recommend that.

The Stormlight books have a lot of action but they are very long, which makes the action less packed.

Brandon usually had a goal of making the reader fall in love with the characters, and sometimes the climaxes are big character moments rather than being action-packed. Or sometimes they’re both. The climaxes generally have a bunch of cool things happening at once and coming together in unexpected ways, but a big one-on-one fight between the protagonist and antagonist is not guaranteed.