Via mrdoob/three.js#9310 and rollup/rollup#774 – V8’s lazy parsing of function expressions is causing Three.js r80 to take ~4x as long to parse as r79. By wrapping the UMD factory function expression in parentheses (see lines 6 and 40881 of the two attached files) we can prevent the function expression from being lazily parsed, with the result that r80 parses faster than r79.
Live demo: https://ns-valtrxdwwc.now.sh/