I totally understand my guild is just behind yours and we regularly bring in a few people every week that don't know the fights and still manage to get at least 4-6/12 done easily. Anyone that complains about it being "too hard" is just being silly entitled pricks themselves. They have every opportunity do get these fights down. I would know- my RL only gets 9 hours a week at all to even play wow and we still manage.
I agree with the idea that 4/12 is "middle-of the road" currently- I don't think you should be comparing yourself to the top 15%, but instead trying to evaluate your progress to guilds who ate 8/12 or even 6/12, the expac isn't coming out for awhile- you have plenty of time to down Arthas and keep busy until then- you aren't running out of content and the content that the 4/12 guilds are running into just takes practice and a little forethought.
I am part of what I would call a very casual guild with some people that like to raid- we have about half our raiding team each week that will switch out for our other raiders. Gearing up for 10 man ICC is cake and we still manage to be 5/12 and we'll probably manage to get 6/12 in the next few weeks and when we do we will be totally stoked about it. The key is it is OUR progression, we don't need nor want any more breadcrumbs from Blizz. There is no huge wall facing guilds in any fight I have seen so far, in fact the only reason we have not gotten farther is we as a group just need a little more practice with the bosses in question. Why would we care about progression if we knew it was just going to get handed to us on a silver platter anyway. Our goal is to down Arthas before the Expac ships and to have fun doing it at our own pace. Everything is doable from what I have seen to even moderately busy people irl- it just comes down to do they CARE enough to try more then a few times and get over the wipes that EVERYONE goes through? It took my guild a very long time to get past Saurfang but after wiping on it enough times for enough guildies to see what they need to do in it we one shot him every week easily and we just got past him very recently. Form what I have seen this content is easy, but the telling factor here is does those 4/12 guilds give enough of a damn to learn the fights through a little bit of blood and sweat each week.