"what's the point if they can be instantly killed from far away?"
The point is the author seriously hates pain, killing, gore, and death and doesn't want it in his setting. Some struggle or hardship is fine to a point but the setting isn't about death or murder. Gratuitous depictions of it also goes against the wiki rules. The setting is about love and redemption. Monsters don't kill or hurt humans unless it's a last resort, they have abilities that induce lust and incapacitate people without harming them.
This is a porn wish fulfillment fantasy and is about having a family with the monster you want to imagine your self with. Not killing people. Due to the history of the English fanbase the community has very little tolerance for the talk of killing monsters.
From the author on why he created his setting:
1.Our society and the aim of MGE
Our society has several merits , but is also an oppressive and nervous atmosphere and forces selfless devotion to inhabitants.So there are people who choose to commit suicide, known as Karoshi(death from overwork and mental stress) .Such atmosphere causes some of us to have a pessimistic view of life. The world of MGE is created for those who are tired of this world and actual women for various reasons, so it is negative to the rule or taboo of the actual world, and MGs are active toward men. We observe actual laws and discipline strictly, and hate to bother others. So we need a shelter in fantasy.
If Japanese MG fans see a succubus, they see her as an liberater who frees them from the choking rules and taboos of the actual world, and lets them indulge in the love and delight of sex. I think it is the reason why the Demon Lord is accepted among Japanese fans.
My goal is not to create a creepy, dark world, in spite of what some of you say.For me, the actual world which commands its inhabitants to die in harnesses is far more creepy and dark.Because it is the system which oppresses individuals, and forces them to live and die for the communal cause, like Lescatie. Corruption is merely used as fetishism.I don`t say it is perfect and beautiful, but MGE consistently aims for the world where one can fall in love with monster girls without being bothered by any worldly affairs.
So, MGE is basically the fruit of "opportunism". The settings are designed to help stir the imagination of the love with monster girls, and it isn`t suited for consideration of realistic integrity.
On the other hand, if the people whose values reflect the actual world see a succubus, they may see her as an evil existence who plunders everything from them and turns them into sex-crazed beasts. For those who make much account of integrity of settings, MGE may seems to be like poor patchwork. It is natural, because MGE is not suited for them.