You want games you buy on Steam to be on Steam and not basically be a key for an alternative storefront
They are on Steam, have profile features and everything else like other games on Steam. The licence you buy is for Steam. They require an additional launcher, the only difference there is that Steam won't download and install it for you like other integrated 3rd party software (Direct X, Redist, anti cheat e.g.). Valve agreed to that and the alternative would probably be: no EA/Ubi games on Steam. If you hate it that much, boycot their games.
The filter right now actually works as it should: I'm a collector on Steam, thus want EA/Ubi games on Steam and only want to see those prices, but not those from EA/Ubi store or key/account linking offers on retailers and key shops. While the general setting unfortunately doesn't affect main and deals pages yet, it does on a specific game page.
The Steam page for Far Cry 6 for example merely states that it "requires an Ubisoft account"
Look at Far Cry 5 store page, there it's described better. Is this inconsistency great? Nah, but that is Valve's/Ubi's responsibility. Should people look up information themselves before buying games? Yes. GG.deals also doesn't tell you whether an old game is broken, can only be played within compatibility mode or have broken achievements. It's about price comparison, not installation advices.
GG.deals could add an additional info field to display that it requires an additional launcher as a service, but don't mix up the platform/DRM filter.