Thank you for your replies and sorry for not having posted it in the appropriate forum. Hopefully a moderator will be able to move the thread.
I kept trying the decks o the trainer too. The deviations that I considered were those that were above around 51% after 15000 games, above 52% for 10000 games or above 53% for 5000 games. I tried removing the Arsenic and the SoSe, but it performs worse against its unaltered version - although this was a few modifications earlier, I will check today in case it is now better to drop them.
EDIT: The original deck wins 87% of the time vs the modified deck dropping both Arsenics, running 5000 games. The original deck wins 54.6% of the time vs the modified deck dropping the SoSe, running 10000 games.
EDIT2: Current improved deck:Hover over cards for details, click for permalink
6qq 6qq 6qq 6qq 6qq 6qq 6qq 6qq 6qq 6qq 6uq 6uq 6uq 71a 71a 778 778 778 778 778 778 778 77c 77c 77g 77g 77g 77g 77g 77g 77k 77k 77k 77k 77m 77m 77m 77m 7ba 7ba 7ba 7ba 7ba 8pm
After one-card improvements, clearly better. Beats the deck in first post 60.4% of the time in 5000 games. It becomes even more stall-ish, beating the other already stalling deck with an
average of 22 turns to win.