Am I ENTJ?

[Ezra]

I'm not one of those who want to defend Socionics at all cost and criticize everyone who are sceptical or don't know the "high" stuff.

Indeed. You reserve it for your own system.

[Ezra]

The one thing that doesn't fit right for me is the fact that ESFj's fifth function is Ti, and I work in IT.

And?

[Charlie]

Well I'm not 100% sure about how the Introverted logic function manifests itself, but I would say I'm fairly good at "understanding logic and structure, categorizations, ordering, logical analysis and distinctions" (Wikipedia) etc etc without external help.

Have I totally misinterpreted the Ti function itself, or rather the nature of the 5th function?

[Ezra]

Watch out for Wikipedia. It'll be 'other system'-ridden. Use Wikisocion instead.