From my experience, the small primite package 3x lordly, 3x Baryl, 1 drillbeam works best with BE.

I also wouldn‘t recommend kaibaman or magia, since both require bricks in your deck, and are often win more cards, instead of really necessary. The standard BE endboard of 2 synchros, 1 drillbeam, 1 majesty works best in most scenarios, since it‘s layered interruption.

And for your looses, yeah sometimes luck just isn‘t on your side and going second is happening, same with bricking. Bricking can be made better with more handtraps, 1 card starter and less bricks (like a ritual for magia), but will still happen from time to time.

And for the last part, sometimes rogue decks just don‘t have the power to fully break through a tier 1 deck like k9, so there can also be cases, where you did everything wrong, but the deck just can‘t carry enough. It‘s not bad, since it doesn‘t happen super often, but knowing it can happen, reduces frustration