Frankly, the Sun Soul Monk in Xanathar's isn't very good. It starts off pretty okay with giving monks a badly-needed ranged attack feature that can hit for (unarmed strike damage + dexterity mod), getting extras by spending 1 ki point or getting Extra attack -- of course, since it's a ranged spell attack, it doesn't stack with Sharpshooter. And it's only 30 feet, anyway. But Searing Arc Strike becomes an increasing waste of ki points (you will not care about spending a ki point as a bonus action for 3d6 damage, dex half, nor about dumping more ki points to increase the damage die by 1d6) as you level. And Searing Sunburst is just curiously bad. It's 150 feet and an action, and it is a 20-foot radiant burst, but it's on a Constitution save (ugh) and does 2d6 damage (UGH). You can spend more ki points, up to 3, for an additional 2d6 per ki point. It's like having a cut-rate fireball, only it targets a much worse save and it eats up from a 4th to a 6th of your resources. Sun Shield is just plain bad as a capstone. Shed light as a bonus action and if you get hit with a melee attack, use your reaction to deal 5 radiant damage plus wisdom modifier.
It's an awful subclass. None of its features meaningfully stack with what a monk typically does in combat and except for Radiant Sun Bolt it doesn't provide options worth the opportunity cost. Don't take it unless you feel that monks are too powerful and you need to nerf yourself.
