berserk VS chess-2

Yep, completely normal. You should now do two things. First try another engine like Ethereal as suggested by IMJorose, Berserk or any other engine; and second, try simulating Chessbase-Stockfish communication by hand.

it's all cool but at stockfish 3 times fishtest racked up insane 30 cores or so :) Overall it growth in strength attracted more people who have more CPUs and it made it stronger which attracted more people etc. At times I started to contribute to sf mibere was considered a god of hardware with 200~ cores running, but now we have noob, technologov who ALWAYS run 4x of this and also mlang who powers up 1000 cores when he feels like it + people like linrock with 100 cores, etc. Sure, it made an impact, but what I'm saying that even at sf 3 times this number of cores was enough to develop it really rapidly. As Tord (author of Glaurung) said making top engine being open-source opened floodgates in terms of progress, because when he started to be intereted in chess programming progress was pretty miserable since everything was commercial and ideas exchange were basically non-existent. Nowadays field is all about open-source, everyone feels free to try other people ideas. And stockfish is like a leading flashlight because truth to be told almost 0 ideas from other open source engines work in it while vice versa it's more of a case. I even talked to other engine devs which resulted in some of my contribution in other open-source engines, in classical eval it was double pawn protection of king ring which spread among I think like 5 engines, now in search it's https://github.com/jhonnold/berserk/blob/main/src/search.c#L565 Also razoring in berserk is based on my form that was good in sf but didn't quite make it, but there it was https://github.com/jhonnold/berserk/commit/3a55e560e0b45900802e424a9c29aecbfd371fe5 truth to be told I have absolutely 0 idea why it was good in Berserk but not good enough in Stockfish but oh well :)

Yes, that is true. One can use NNs in either evaluation or heuristics or both - to my understanding, I haven't researched this that much. But yes what you say would fall under the heuristics category that mainly drives move ordering, better looking moves first. As the search is ultimately a depth first in basically every engine. If you are curious, allow me the shameless plug, you can check out my engine @ https://github.com/phaul/chess-2 I'm happy to answer you anything else about the engine, I love talking about this stuff :)

If you decide to implement all rules ( en-passant / castle etc ) I recommend implementing a simple recursive function known by chess engines as perft. (https://www.chessprogramming.org/Perft#:\~:text=Perft%20is%20mostly%20for%20debugging,functions%20work%20correctly%20or%20not.) Running perft on different positions to a certain depth and then comparing your numbers against perft in stockfish etc is really helpful shaking bugs out.For my pet project engine I wrote some shell script that is supposed to debug and find positions where the engine has a bug in the move generator https://github.com/phaul/chess-2/blob/main/debug.sh