Examples of heuristic engines are Hans Berliner’s CAPS-II and PARADISE by David Wilkins. PARADISE used a database of 200 rules.
There are also engines that try to retroactively apply rules to Stockfish evals but they’re fairly confusing in my experience. It’s like being told the answer and having to come up with a reason after the fact.
Imagine if LLMs were the only way we had to play chess. You’d need a centralized server and peak performance wouldn't even best a grandmaster. You spend $1 trillion building a super cluster because that’s all you know.
< - - This is where AI is today.
And then some startup creates Stockfish, a chess engine better than any LLM or grandmaster and can run on a smartphone.