I think this is only true if you remove any mechanical interventions from the equation. For example, we can be pretty confident that any positions that require a Sybian probably didn’t exist before electricity. Certain positions that require vibrators or even dildos probably weren’t practical before we learnt how to injection mould silicone. Stuff like Japanese Rope Bondage was probably around but the explosion of the internet has probably created brand new knots and positions that were far more advanced that what was previously being practiced. Maybe furries existed in some historical cultures but certainly not with the level of detail and technical innovation of modern fursuits and it’s hard to imagine there ever being such a vibrant culture prior to the internet allowing furries (or other sexual minorities for that matter) from finding each other and creating entire sub cultures.
I think if you restrict yourself to two adults in a bare room with a bed and maybe a chair or two, then yeah, most of the things a modern couple could do now were probably known 500 years ago but sex is a much more expansive activity than that and many of our modern expressions of sex would be pretty alien to our historical ancestors simply due to the resources we have easily at our disposal.