JITing html template files
jinja2 is robust enough to render templates responsively but the problem is seen when you have a heavy/blocking tasks to process (requesting database, bulk operations ..) before passing variables to jinja2 to render templates.
so with a good application design comes a good performance.

add caching support, use 3rd Flask extensions like flask-caching
use Task Queues apps (like redis or celery ..) to handle asynchronously in  background a long-running jobs that would dramatically reduce the performance of an HTTP response
use an HTTP accelerator like varnish
Many people use jinja template rendering for their web base apps.
A high percentage of apps have a few templates but when the app gets popular,  templates will be processed many times.
I wanna to know that is processing the templates a bottleneck as app gets more hits?