Sorry for necro-ing this (it's still near the top of the tips forum and I ran into the exact same issue and it almost drove me mad):
The reason your lighting (or anyone else running into this) looks so different is because of the exported quality settings for WebGL builds. You can fix it by using deferred lighting, which makes lights much more efficient (but can't be used with an orthographic camera or for certain lighting effects), or by bumping up the number of pixel lights allowed in the player quality settings:
https://forum.unity.com/attachments/qualitysettings-png.203841/
Pixel lights are pretty expensive on performance, but so long as you aren't pushing the boundaries anywhere else you should be okay (I would try deferred lighting first though). I bumped up the pixel light count for my game Archipelago (up to 12, I think) and it looks pretty close to how it did in the editor: https://gedig.itch.io/archipelago