I am right now profiling and debugging a new theme we are developing. I use the shopify chrome extension to get details about the time spent on code fragments.
I noticed that our new theme (in development environment, separate dev store) is using renderer "Rendering back-end: core". Seems that the storefront-renderer is much faster.
See official statement here https://www.shopify.com/enterprise/reunite
It seems our store uses different render engines per page. Thats why I am asking. Have no idea on how to isolate the problem any further. Advice on that would be welcomed.