OK, first of all, Gateron Yellows are already fairly smooth. Not perfect, but smooth by Cherry standards. People who lube them to their preference tend to report a noticeable improvement still. So as you test your switches, you should be noticing improvement with the Yellows if lubed properly.
Switches take to lube differently. For example, most people report that some low-tactility switches like MX Brown and Aliaz don't benefit much from lubing. It can even remove their already-limited tactility. BOX switches, like BOX Browns, aren't usually lubed, and can lose their lube.
But heavier tactiles can benefit
immensely from lube. MX Clears, for example, are stiff and scratchy. But if you wear them in for a month and then lube them, they become much nicer to work with. If you are using lighter springs to build Ergo Clears, then lubing becomes essential: the spring needs to clear the tactile bump while using less energy. Proper lubing then becomes an enormous factor. Likewise, if you are building Holy Pandas, you don't want to use them unlubed. Proper lubing makes an enormous difference to the typing experience with those as well.
Alpacas and several other Durock linears come with a light, but consistent factory lube. This prevents scratchiness and makes them feel smoother than many other linears. Regardless, people still film and lube the Alpacas. The film reduces wobble and improves the sound, and likewise the lubing is a factor in improving sound and optimizing smoothness. So the user modifications to the Durock switches, in terms of filming and lubing, actually become pretty decisive towards them becoming an endgame switch.
As far as Topre goes, I've always found that the EC switches have a tactility that is present through the entire keypress. So this contributes towards a feeling of 'smoothness' because it's not just a scratchy linear with an interruption [bump] somewhere along the way. Nonetheless, people often lube Topre, because they think it makes it smoother and sound better. I personally thought that lubed 45 G silenced Topre was great. It's an entirely different mechanism, and the rubber-dome is providing tactility consistently throughout every stage of the keypress.
For a more 'linear' Topre, you might want to try Niz Plum switches. I reviewed a 45G keyboard with them here:
https://geekhack.org/index.php?topic=106707.0I want to try 35 G next, as that is probably closer to the resistance provided by MX light tactiles.