I think that just changes the default game resolution value as opposed to scaling down the game. Well at least that's what it did the last time I checked it & as a result all scenes became scrollable & half my menu was hidden.
Manual scaling down of graphics would actually be relatively quick as you could use XnConvert to batch scale & convert all png files in each folder to webP in a matter of seconds for each folder. Once you'd converted all image files to webp it would be a matter of opening up your ved file in sublime text, atom or notepad++ & doing a search all for .png & then replace all with .webp. Again matter of seconds. But it would still be a lot of work.
I recommend just reading the article first or at least focusing primarily on the windows &/or mac versions of your game, before messing about with the mobile platforms unless your intention is to only release to the mobile platforms. The reason why is also explained in the article & it does actually have a very valid point in that flooding the market with too much choice all at once spoils the chance of sales for other platforms. i.e: win & mac titles usually have a higher RRP than mobile platforms, so most people would probably opt for the cheaper mobile platform version if released at same time.