Negativity? I'd call it staying realistic. It's working so far. Keeps me from being disappointed because people overhype everything nowadays. EotL learned many people that same lesson.
End of the Line promised cosmetics, a terrific SFM, and a new map. We got cosmetics, a terrific SFM, a new taunt, and the coolest-looking action item of all time. It was disappointing that Valve decided to pull Snowplow at the last minute, but as long as you kept your expectations reasonable, it wasn't nearly the massive disappointment that everyone makes it out to be.
There's a difference between keeping your expectations
reasonable and keeping them dirt low. For example, I expect Valve to release an update in the next week that brings competitive 6v6 matchmaking out of beta, possibly with a small cost to buy in, as well as a good number of weapon changes with varying degrees of success,
maybe a new taunt, probably the release of a community-made map or a map brought out of beta, probably the addition of the new PASS Time map that the devs have teased, and the introduction of a summer-long campaign with a unique theme (matchmaking, Robot Destruction, Alternative maps, etc.) that helps it stand out from previous contract campaigns. Valve will probably surpass these reasonable expectations in some way or another, but even if not every one of them is met, I'll still enjoy the update for what it is.
Yes, expectations for an update should be handled appropriately, but in my opinion, hyping an update out of the moon is only slightly less "appropriate" than expecting the absolute worst possible update every time. When I go to a decent restaurant, I don't always assume that the food will be burnt to a crisp; I assume it'll be a decent meal, and handle any fallout like an adult.