You must have read mostly his very late stuff. Little of his early to mid career work went there - on the other hand, the ‘orgy’ books seem to have been prescient about how society is going anyway.
You should probably go give The Moon Is A Harsh Mistress a try. It’s available in eBook format cheaply from the usual sources. The math and physics in the book are dead on - and if you weren’t alarmed about the US’ retreat from space and current cession of the moon to the Chinese, you will be afterwards. Heinlein spent the rest of his life after the Apollo program ended up going nowhere desperately trying to get the US Government to realize what they’d done. Thanks to Democrats like Senator Proxmire, most of the government still doesn’t know or care.
There was some sex as far back as Glory Road, or even earlier in Stranger in a Strange Land, but it didn’t get graphic until the mid-70’s with the Lazarus Long stories and then Number of the Beast and Friday.