Are stick and powder sunscreens as effective as lotion?

No, they’re not as effective on their own because you can’t apply them as evenly or thickly. Powder sunscreens deliver much lower actual SPF than advertised—you’d get SPF 15 or 20 from an “SPF 50” powder. Sticks are better but need multiple passes. They’re fine for reapplication over makeup, but not a replacement for lotion.