Background
Rank 1 Vale of Eternity player here with top performance across Arena (when I try), Tournaments, and general Elo for a ~1 year period.
I had a pretty strong baseline before BGA by playing 2p IRL with a fellow competitive gamer, TCG player. Was in the 300-350 Elo range during the early rating adjustment period.
I would befriend my high rated opponents after playing against them to discuss the game we just played and general strategy/card evaluation. I was a tryhard that analyzed my losses for mistakes and looked for adjustments (I still am, but I was back then too). By learning from every mistake early on I was able to reduce my mistakes quite a bit which took me to the 450-500 Elo range along with other top players. I work in STEM which seems to be a common trend among many of the top players, high analytical thinking combined with the drive to compete.
What took me to the next level to the 500+ Elo range and beyond to record setting Elo (600+) strength was all the external work put into the game. I often joke that it takes writing an entire strategy wiki website to truly reach rank 1 in a game because that is what happened. The more I would write in detail about the game the better I would get. Thinking deeply about the game and clearly articulating your thoughts will improve your gameplay, often at a higher rate than just playing. The same is true in games like Chess where playing can only take you so far. Studying helps compliment playing.
I created
https://valeofeternity.wiki.gg/ and have written over 80% of the content on the website. The biggest value on the site is the card image galleries since there is no other convenient source online and no built in tool in BGA like there is in Zenith for some reason. Look up any cards I list here if you are curious.
General Advice
Vale of Eternity is pretty deep so to get good at it you would need to know the game very well from many repetitions and develop your own optimization system that gets calibrated over time. It is an open drafting game so most of the skill is from card evaluation and picking the right cards with both players in mind. Learn all the main combos and synergies, then develop a baseline evaluation for each card across various stage of the game and a system to adjust the card evaluations for both players based on the board state and make all your card choices with these adjustments in mind.
More specifically I'm sure I evaluate and use the universally strong cards like Undine Queen, Valkyrie, Freyja, and Eternity similarly to other players. Not much to optimize there, the cards are easy to use and quite strong over 80% of the time. The biggest difference in play style is how myself and other strong players are able to fully utilize the full 70 card deck, even the weaker cards when the opportunities arise. Since we can utilize a higher percentage of the deck effectively we can "make lemonade" (a winning game plan) consistently with less reliance on lucky "flips" or draws compared to more average players.
The most generic Vale of Eternity example I can think of is that the expert player will tame (hold onto) a variety of scoring cards in the early to mid game even if they seem fairly mediocre (average baseline, low synergy) because they understand the value of holding cards early for the
potential for combos/synergy even if they never show up and also understand the game is fundamentally about points and you
need to draft point scoring to win. Many average players will oversell potential scoring cards earlier on, make a fantastic stone economy, then fail to acquire enough scoring to reach 60 points by Round 8 (a requirement to be "good" at Vale because they were praying the RNG gods for the perfect scoring cards to arrive at the perfect moment for them in the late game rather than picking it up earlier and holding onto it.
The expert player likely leans more towards stockpiling points and will often accumulate 60 points or close by Round 6, then will spend the remaining of the game figuring how to execute that winning 60+ point game plan ASAP by sequencing summons and selling in the late game or looking for ways to improve their scoring position or find opportunities to completely cripple an opponent by first picking (blocking) a key card. Expert players are generally less affected by blocks since they create more consistent game plans that are less reliant on specific key cards. An average player might be relying on one of 3-4 cards remaining for them to first pick in the late game to secure a winning score, but an expert player is looking for one of 8+ cards remaining for a win.
More Specific Example
Examples of high scoring cards the expert players will onto more often average players to "hold points" include Tidal, Rock Golem, Rudra, and Aeris. An average player will often 2nd/3rd pick Tidal (5 cost dragon instant, score 5 point per dragon in your area/summoned) in the early game, but sell it rather than tame it to help their stone economy in the early game, but without having a way to get immediate value from the sell like an early Troll or Valkyrie to earn points every round off the sell. Without a real reason to sell Tidal already in your hand it will often be better to just hold onto (tame) Tidal instead. Tidal has a pretty high ceiling, it is quite busted with other dragons.
The average player thought process may be close to "this Tidal is only worth 5 points right now and I don't have any Dragons yet so I might as well sell it" and they do this with Tidal often enough that they hardly ever get to use the card. They only get to use it when the stars align perfectly with dragons already in their area and they have a chance to first pick it because opponents would surely block a scary late game Tidal and at least get sell value from it.
The expert player thought process would be closer to "this Tidal is only worth 5 points right now, but if I tame it every dragon is worth 5 more points. All I need to make Tidal playable is 1 more Dragon so it scores 10 points. A 15+ point Tidal would be devastating and Tidal gives me further combo potential with Scorch/Aeris/Willow. I already have Undine for stone generation so don't need to sell a dragon."
Many strong scoring combos in Vale are quite unlikely to naturally pull off for a player unwilling to hold onto specific key cards in the early game.