"Necropolis" - changes to creatures of levels 6-7.

maps similar to the one I provided as an example exist, and they also have Multiplayer, and they cannot be completed in 6 weeks. For example, look at this one, and you will see that it is impossible. I played it with my friends for about two months (we didn't finish it...) and there was clearly a lot left to do - it's a large map, with heavy guarding at the exits, like 20 dragons, 40 witches, 50 hydras in one army.

Added 1 minute ago
a great new world also probably won't be completed in 6 weeks.

I think we've strayed from the topic, and you're mixing up the concepts of "completing a map" (single-player) and "defeating an opponent" (Multiplayer). The first can take a very long time, as you have to defeat all the mobs. Regarding the second, in all the Multiplayer tournaments I know of, according to player reports, games almost always end within 6 weeks. Therefore, balance for longer timeframes is not even considered in balance mods.

well, here's BD -11, it just happened

I wrote above, even if it's -999. In practice, the real BD is ultimately capped at -5, and it is this value that is taken into account when calculating the damage.