The functionality to filter by system has always felt a bit flawed to me, as you get results that overlap highly frequently on certain systems. One basic example would be Gamecube/Wii.

If you filter by Wii, almost all the top results are Gamecube games that you can also play on a Wii because of backwards compatibility.

This makes discovering Wii exclusive speedruns substantially more difficult, as you have to wade through a sea of Gamecube games to find just a handful of Wii games.

Another problem is how Cover Art doesn't reflect what system that game is on. So sometimes you'll get raw art with no markers to signify what system it is on, to then click on it and find out it's not on the system you're looking for. This makes discovery further obscured.

All this doesn't even touch upon the games that get added with a dozen or more systems listed underneath. Who actually finds benefit from Super Mario Bros. 1 being sat at the top of the list for every Nintendo system you can name? It just gets silly!

I get where you're coming from with this, but there are really not very many games that are exclusively playable on a single platform these days, with re-releases, backwards compatibility, official emulation, cloud gaming, etc. By your own example, there's really no such thing as a "Wii exclusive", since (almost?) all Wii games can also be played on WiiU. I suppose you could have an option to explicitly exclude certain platforms from your already-filtered results, but tbh that just feels like a clunky band-aid solution.

I think the problem is more with how the site handles platforms in general. One thing that might help is if there was some kind of distinction between release platforms and play platforms, but even that could get a little confusing in some cases (e.g. is the WiiVC version of SM64 a new release? Or just another platform you can play the N64 game on? There's no right answer).