It is not accurate to claim that chess is already ultra-weakly solved and that the game-theoretic value of the initial position is a draw. While it is true that the game of chess is generally thought to be a draw when both players play optimally, this has not been proven and it is still possible for one player to achieve a winning advantage through superior play.
Furthermore, it is not possible to fully solve chess in the sense of finding a winning strategy for all legal positions, as there are too many positions to consider. The number of legal positions in chess is estimated to be around 10^44, which is far too large for current computers to analyze and calculate strategies for.
It is also not accurate to claim that weakly solving chess would require calculating 10^17 relevant positions, which present computers could do in about 5 years. This claim does not take into account the complexity and depth of chess positions, and it is likely that significantly more positions would need to be analyzed in order to find a satisfactory strategy.
Finally, while it is true that pruning, the "best first" heuristic, and game knowledge can be useful in the process of solving a game, it is important to recognize that these techniques have limitations and may not be sufficient to fully solve a game like chess. Ultimately, the process of solving a game like chess is a complex and ongoing endeavor that requires a combination of mathematical analysis and understanding of game principles and tactics.
You don't understand what Schaeffer did. He would tell you where you are going wrong if he had the chance.