Actually the stock bushings are the ones that fell out when I took my arms off for the first time. You're right though, the replacement material is harder. I have had maybe one or two that were hard to get out and even then I could just grab them with some pliers, turn and pull out.
I have had good luck with an air hammer with a punch adapter and catching the edge from the inside, but if you dont have one that dont help you much but they are only like twelve bucks these days at hd or wally world.
I've taken several sets out and I have had little to no trouble with them as well. I wonder if the early model ones (like FX400 & early Cannibal) have different bushings? I removed mine with a big punch and hammer as well. Usually two whacks with a hammer and they are out.
I have had some that had to be taken out with a hammer and screw driver. They were completely siezed in there and spray oil wasn't penatrating quick enough.
I've had them really tight, too. I went with pliers but that's gonna' leave some marks. Grab 'em and turn. They'll come out. After one is out, I use a socket to push the other one out.