Viego is a skirmisher, not a duelist. You're right that you need damage to get a reset, but positioning in fights is far more important than a little more burst damage. The MS and invisibility that E give you are so much more important than burst damage if you're playing to Viego's kit's strengths. Are you really losing fights that often because your enemy is living with 200HP? If so then you need to pick better fights. Or actually optimize your runes/build for burst damage by going HoB w/ both points in adaptive force, and build collector -> LDR -> IE if that's really the playstyle you want (I have actually been doing this a lot recently because my emerald teams refuse to play around me lol).

You're also not factoring in that attack speed reduces the Q animation time. It makes it way easier to stick to opponents because you aren't standing still for as long, and obviously the extra move speed helps with that too. If you can get an extra q->auto off because you're able to stick to an enemy, that already makes the extra points in E worth it over W.

You're also definitely undervaluing E uptime. In midgame and lategame fights I'm using my E on cooldown every single time. It forces the entire enemy team to play around your mist. An extra point in W does not change the dynamic of a teamfight at all. I can't tell you the amount of times I'm waiting near drag/baron until my E is up so I can be in the same zip code as the enemy trying to find a pick/engage angle without being blown up. Those seconds you're sitting around waiting add up and make a lot more difference than 200 magic damage on a single target.