@Nyayan
There is no such thing as "give+take" action for a male MC using the latest public version. I have no idea if you have it because female MC or because you are playing the latest patreon version.
Also, there is no such thing as specifically a foursome option, only "threesome" and "all" (which could coincidentally end up as a foursome if all has exactly 4 participants unlocked).
As for all, it explicitly warns you that it causes permanent damage to the slaves and also costs a magic potion that you won't be able to get until late game, and even then costs money to make. If it didn't cause permanent damage and didn't require a potion then it would have been an actual viable strategy.
Furthermore, it takes a very long time to unlock a bunch of participants for the "all" option and then grind their affection to the point you unlock group sex with them.
By the time using "all" to grind mana becomes viable you would have already gotten your team to be amazing melee killers that instagib all enemies in melee, equipped from head to toe in supreme gear... so while this late game strategy makes it possible to cast spells in combat without grinding sex for a week to pay for it, by the time it becomes available you have no reason to actually cast spells in combat at all.
It is also worth mentioning that even with unlimited mana, fighting with magic is very inefficient without first raising agility which raises both your offense and defense. So once you do that you win combat anyways and the magic is redundant beyond roleplay value. It also deals way too little damage for the fact it costs mana and can miss... so there isn't even that strategic aspect of "ok, day 2 of the game, I am getting my butt kicked but I can salvage this if I burn mana to repeatedly mindblast them". even with a few levels in magic affinity you are too weak to blast them effectively.
... that all said. it sounds to me like you are playing latest patreon version and that it simply happens to addressed that issue already by allowing far more mana generation.