I feel some guilt about the current state of affairs. A team I led ("Parkour") built an early (the first?) ES.next -> ES.now transpiler -- "Traceur" -- in the ES6 timeframe...so to some extent, we started this fire.
And it is on fire. I see so many traces where the combination of Babel transpilation overhead and poor WebPack foo totally sink the performance of a site.
I'm happy that babel-present-env is now the norm, but I'm sad that we're still playing this game. To some degree I think it would be prudent for most developers to make a hard cut: only support browsers that support ES6 natively and give other users the progressively-enhanced experience (which you were doing, right?). Transpilers should fade away, not get more central to our workflows.
I less kind thoughts for proprietary, non-standards-track forks of HTML and JS (e.g., JSX), but will keep them to myself = )