Let me start by introducing myself. I played Battle Forge since it released and returned about 1 month ago. Without previous knowledge of impactful cards for PvE and knowledge about the basic mechanics of this game ( right camp from tower spawns waves, nature for hand holding shamans till end game, mass cc to take objectives first, void pool management, .... ) the entry skill level for this game is insanely high. In normal RPvE 9s I encounter way too many players who fear to loose their troops when taking a camp, so they stack army instead of learning how to micro or efficiently utilize what they have. The rank says nothing about a player efficiency in RPvE sadly.
On the 5th day into the game I cleared the full campaign on advanced, about a week later everything on expert. Today I cleared everything which gives a card/booster beside Promo WBG.
It is possible to clear the start camps with all 4 elements. I've seen people who previously kick me out of lobby, because I had a lvl 60 deck and silver rank in rpve 9, play in another match with me and wait till they have a harvester to clear T3 camp although I ran Fire and basically solo it or ran Frost and homesoil it clear.
RPvE 10 is anotehr beast, it raises the difficulty by 1000% while rewards are maybe 10% better. In 9s you don't have split starts or both camps directly at your orb, which needs the other 3 to help you right at the start. Rarely I get a random lobby where players don't play egositically hoping to succeed alone. The only lobbys where I somehow can expect people to use teamwork is when i see multiple Fire start decks. It somehow is a unwritten rule that people help each other out with ( super expensive ) mine or/and (cheap) eruption.
The achievment took me about 2 weeks. It is unreasonable to ask a real beginner to reach that level ever, without putting in real effort and watch guides, videos which are badly voiced by mostly germans havin a bottleneck weird accent when talkin english xD.
I bet 80% of those gold rank and up, are not actively reading up on forum or guides and just play the game as they like = won't ever succeed in 10s without being carryed while not even realizing they are carryed because they succeeded with Lost Ships without wheels and the energy somehow never ran out, but that only happens when somebody plays fire.