@dexdoujinmanga It's not explained clearly in manhwa, but at least strongly hinted in the novel - but there is something like "the path of hero". It's not tangible, but rather breadcrumbs trail made of quests, fortunate encounters and powerups, that, if followed clearly, will lead one from royal castle to easily defeating Demon King (but takes 10 years).
Why it exists will be revealed in the future, but basically, high evaluation of Sieg is a result of him being the type to blindly follow the rut (which is something teaching staff appreciates immensely - because it lets them be lazy), while MC strayed in first run (which actually resulted in his experience being way crappier than intended) and downright avoid it in subsequent runs.
As to why he refuses to follow the way he knows leads to success - it's because it takes 10 years. MC finds that absolutely unacceptable.
he does actually speed run it at one point literally doing it the day he is summoned and gets neutral in everything but the staff still fail him because he didn't do it their way
If people/readers don't realise by now that he is currently only FF-Class in his results, so after he is finish this run he'll finally be the true FFF-Class Trashhero as the title clearly states...it'll be quite interesting to see what he'll do on his next run. maybe just give up and not do anything??
@Zyscheriah Chapter 34 in the web novel. The manwha didn't skip any critical parts as far as I could tell. The novel just explains everything in more detail, especially the thoughts going on in Han Soo that make him do what he does and skill explanations.