I entirely understand that people might not like Robin's song, but
you're saying a lot of things here that are simply factually incorrect. Firstly, how on earth was Russia's 2014 entry overrated by fans? From memory it was mid-to-low-table for most fans, and the poll on this forum reflects that; in spite of that, it ended up coming 6th in the final, so if anything it was
underrated by the fans (though in saying that I don't much enjoy the song myself). The same is true, to a lesser extent, for every other one of the examples that you mentioned - you can't really say the fans overrated them pre-contest when they either equalled or beat fan expectations in May. Better examples of songs 'overrated' by fans would be Israel 2014 or Iceland 2016, which were loved by many fans but flopped - and I don't exactly think you can say the forums have some sort of massive political bias in favour of Israel or Iceland.
Secondly: it's simply wrong, in more than one way, to refer to 'these countries are just trying harder' as a 'strawman argument'. I mean, to begin with,
'strawman argument' isn't just a term for 'argument I disagree with'; it has a particular meaning, which is completely unrelated to how you've used it here. Specifically, it refers to misrepresenting your opponent's argument - and so in this scenario is entirely irrelevant, since 'they try harder' isn't a reframing of an opponent's argument at all but rather a point made completely off its own back.
Getting to the main point, though,
it's pretty undeniable that they are trying harder. Just compare Sweden's massive-scale annual Melodifestivalen NF, or Russia sending superstars backed by multi-million dollar staging budgets, with the 'just take whoever's willing to help us fund things and plonk them on a mostly-empty stage' approaches usually taken by Croatia, San Marino and the like. There's a rather obvious difference in the way that certain countries go about these things, and that leads to a clear effect.
To approach it from a different angle: look at Bulgaria. Previously they were one of the 'low-effort' broadcasters just sending whatever, but this year and last year they've started to try a little harder, upping their game with strong songs, decent artists, promotional campaigns and more. That extra effort gave them their best ever score in 2016, and on most predictions they're likely to equal or beat that this year. Clearly the level of effort, then - and of course a good song - are the most important metrics by far? It's not exactly like Bulgaria made some massive transformation from 'politically loathed' to 'politically loved' in the space of a few of years. I could give more examples here if you'd like, but I think you get my point.
And yes: I do think that San Marino would qualify with this song. Easily. They don't have consistent low scores because they're San Marino; they have consistent low scores because they always send dated Ralph Siegel tracks with minimal staging, which isn't exactly a recipe for success in modern Eurovision. Even then, they qualified with Valentina's second attempt, and came close in both 2013 and 2016 , so they actually don't do quite as badly as some people seem to think. If they can sneak into the final with a forgettably-staged Siegel track, they would absolutely make it there with a slickly-staged mainstream dance pop song like I Can't Go On, and that applies regardless of whether you personally love or hate what Sweden's doing here. I'm not saying that politics and biases aren't in Eurovision - because of course they are - but they have a much, much smaller impact that what you seem to be suggesting.
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