You are absolutely correct - nothing is a substitute for good profiling, and everyone should become familiar with ways of profiling their application. (The same goes for testing, too.)

However, there are certain constructs which are known to be performance hogs. For example, using $sth->fetchall_arrayref({}); is practically the slowest way to get data from a database, when compared with other methods. Another is H::T's global_vars, as you mentioned. These don't need to be profiled because they are known performance hits.

I would suggest merging our two approaches. Setting up a good profiling scenario can be time-consuming. In my experience, tackling the usual suspects has almost always provided enough improvement without needing to do a full profiling of a webapp.

However, after hitting the usual suspects, profiling is most definitely the way to go. And, frankly, I'm not surprised that output generation is expensive. But, I suspect that most webapps are getting bogged down in other areas.