Who is the balancer between page speed and an attractive UI?

I believe this can be reframed more productively, since: a) page speed is a so-called hygene factor, i.e. there's a limit after which users get frustrated, and below which they don't think about it too much. Say, around 1-2 seconds for a page/component load, on average (depends on specific context of course). b) UI "attractiveness" cannot be measured objectively, let alone numerically (alright, a questionnaire, but then all will depend on the exact wording), while speed is a very concrete parameter. c) speed vs "attractiveness", whatever that means, is not necessarily a dychotomy - you can have a very usable and eye-pleasing interface without the speed penalty. So it's rather two questions in one, and they are more orthogonal than competing: - how do I ensure the product's speed is below the threshold that makes it annoying? - can I make UI easy to use and pleasant to look at without making the backend much more complex and processing-hungry?