It is worth mentioning that some of your math in the initial post is entirely wrong.
First, to find the adjusted XP value of the monsters, you multiply their total XP (sum of their individual values) by an amount shown on DMG p.82 (x4 for more than 14 monsters).
Second, if you have a large group (8-9 players qualifies) you use the multiplier from the next step down (x3 for 11-14 monsters).
So your 4 Ettercaps (CR 2, 450 XP ea) and 12 Giant Spiders (CR 1, 200 XP ea) encounter does not come out to 4200 XP, it comes out to 12,600...
It's a 12,600 XP encounter for balance & challenge purposes (well over "Deadly", which would be about 9-10,000) that actually rewards each player only about 500 XP (based on the monsters' actual XP totals).
The amount each player should get per day is based on the effective XP, not the monster's actual XP, so your 12,600 encounter divided by the 8 players means they're each getting 1575 of their daily recommended 3500... probably not worth it from their perspective, since it's only providing 1/15th of what they need to reach the next level (525 XP, but they need 7,500 more to reach level 6).
4 ettercaps & 12 giant spiders- 12,600 effective XP
2 wereboars & 6 giant boars- 9800 effective XP
3 wyverns - 10350 effective XP
Coven of 3 green hags- 8100 effective XP
12 harpies & 1 harpy queen (custom CR 6)- 11750* effective XP
(probably less, since the CR 1's are largely irrelevant next to a CR 6)
Hope that helps.