I don't think you are anywhere close to realize how difficult it is the current challenge for players with only 1 or 2 Heroes. Sure it is pretty doable for very active players. For average active players, slightly harder. For casual players, no way for them to complete unless they spend quite a lot more hours than they normally do.
See as TH8 where only 1 Hero per base, you will required to hit 40 times in 3 days, that is provided you could kill a Hero in each raid, which means it could go to 50 attacks for TH8. Since when we have a challenge where you are required to hit 40 times in 3 days. For TH9 it is simply 20-30 attacks in 3 days.
There are of course other ways to complete the event, as someone cleverly mentioned snipping BK with Minions or Dragons whenever they see an unprotected BK. That is definitely a smarter and faster way to complete the event, but still for average players that is still require a lot more effort than they usually spend on any events in the history of Clash of Clans.
Why not scale it up then? How about TH13 required to kill 160 Heroes in 3 days? Difficult? That's actually about the same difficulty for TH8 to kill 40 Heroes.
I am a TH13 have no issue with this event, but I could clearly see the difficulty for TH8 or TH9. If you think "no, that's cool and SC is doing a good job with not scaling it down for lower halls and there shouldn't be any issue for lower halls", then obviously we don't share the same opinion.