It was only a smart part of his contribution, but it's going to be lots of fun to see people complain about how it's possible that the VFX are worse, even with a bigger budget.
Tim Miller's expertise allowed him to make sure that the effects would be top notch even on a small budget. They started editing the movie while filming, so that by the start of post-production, Miller would have a good idea of what Colossus shots he needed exactly, so he wouldn't waste any time of tinkering with stuff half-through, and could instead focus on perfecting the effects.
And lots of companies and artists actually bent over backwards to get work done on
Deadpool, just because Tim Miller is such a well-liked and respected guy in the industry.
And let's not forget that Miller is a HUGE comic book buff, so he knows Deadpool and his world as much as (if not better) than Ryan Reynolds and the writers.
Don't expect another director to put in as much love for details as Miller.
This sounds like Reynolds is having a major 'Kevin Costner moment' here.