Cached rendering of clips slower than preview?

Hello, I'm Nathan Buckley, nice to meet you all. I recently bought Resolve 17 with the speed editor to do all my content creation for my Youtube channel and I hope to get good at editing so I can produce decent videos, but I'm still pretty new to all this so please forgive my naivete / stupid questions.

One thing that confuses me right off the bat is why the preview of a transform is faster than the rendered version... is there any way to prevent the cache rendering for specific types of clips (i.e. text/titles/images), or at least individual clips? See this video I made to show what I'm talking about:

Update: I've been playing around with Playback > Render Cache > User and manually selecting which clips get rendered, so at least I can choose which clips have the render playback, but in generally the playback doesn't seem to actually be helped with caching -- they still skip quite a bit. I have also tried playing with Timeline Proxy Mode but it doesn't seem to make any difference. Are there other performance improvements I'm missing? I'm a bit confused also about the difference between the render cache vs "Generate Optimized Media"...