I wouldn't say "almost always happier than giga slayers" but there are certainly diminishing returns to the lifestyle.
Having sex twice a month is staggeringly better than having sex once a month. Three times a month is hugely better than twice. Four times is moderately better than three. Five times a bit better than four. Six only slightly better than five. Seven barely better than six.
Dating a girl who's a 4 is staggeringly better than dating a girl who's a 3. Dating a 5 is hugely better than a 4. Dating a 6 moderately better than a 5. Dating a 7 a bit better than a 6. Dating an 8 only slightly better than a 7.
Point is if you're churning really hard to have sex with hundreds of beautiful women per year, you are probably not getting a ton of value out of it, and should probably reconsider your returns on the lifestyle. And when you see guys who are fucking 20 girls a month when you're only fucking 2 girls a month, know that they're not 10x happier than you despite fucking 10x as many girls.