[smolder]

Saying JS improves the experience in terms of speed is too general. Doing async requests can result in faster interactions than whole page reloads, but big JS blobs that offload work to the client can make initial page load take forever on small pipes and can make weak CPUs struggle under the weight. More CPU utilization also drains battery, which does harm UX. Ignoring low bandwidth and underpowered hardware is fine for some products, but a common mistake with many others. People with slow internet and cheap devices are people too, ya know?