Anti-drone lasers can help take down drones for much cheaper than missiles, but have limitations, including: needing line of sight, not working as well in certain weather conditions, possibly having trouble with drones made of laser resistance materials, and having trouble targeting maneuvering drones in the real world.
Putin doesn’t want to use nuclear weapons. If he did, he risks the destruction of his country. Putin, like the Soviet Union in history, uses nuclear weapons as bluster to threaten countries whose leaders and people believe the likelihood of Russia using nukes is higher than it is. Trump is scared. He’s happy to use or threaten military force against countries without nukes, but Russia invades its neighbor in a war of conquest while committing many atrocities, and Trump is obsessed with peace, even, at times, weakening support to Ukraine to appease Putin. Letting Russia gain things with nuclear threats increases the incentive for other countries to get nukes, and one of those countries may be more willing to actually use them.
Russia’s S-400 anti-air missile batteries are good, but without being integrated into larger defense systems, are vulnerable to air power. U.S. air power out-ranges these missiles, and low flying aircraft can’t be seen because the S-400 by itself can’t see over the horizon.