I suspect the problem with impacts not working for some folks is that most folks don't buy very good impact wrenches. There are so many on the market and most aren't even close to the strongest in their class. 200 ft-lb craftsman anybody? It's not often that I see an impact gun in somebody's aresenal of tools but when I do it's usually a POS.
Just my $.02. I haven't found a bolt my 1000 ft-lb nitrocat didn't like. Best $110 I ever spent (got a deal). Quiet too. Higher cost doesn't necessarily mean better with air tools.
Starter bump with a good, charged battery and a good 6-pt impact socket is probably going to beat most folks' impact guns. Built in SHO impact, lol. Just do as has been said and position the ratchet so it can build momentum. Repeat as necessary. And don't forget to clean up the bolt if rusty or mucky before reusing and coat it with anti-seize to make things easier next time.