Pollock has done likewise; Vettori very, very nearly has. This shows it's perfectly possible. Of course only the most exceptional bowlers can do it. I certainly never once suggested that to be even decent you have to go for <4-an-over; ever since about 1990 that's been the realm of the exceptional. The decent bowlers tend to concede 4.1-4.4-an-over or so.
Of course it is. I'd say it's fairly obvious there've been a large number of very poor ODI bowlers in recent years. Look at
this list. Also there's a few names in there who have not been used properly and have thus not maximised their economy - Bond, Flintoff and left-arm seamers Bracken and Bradshaw to the fore. The number of "decent" bowlers in there is not considerable - Harris, Gillespie, Harbhajan Singh, that's basically it. There's also Oram and Vaas who tended to be capable of being very good quite often but also absolutely awful from time to time. There's also some bowlers who were once very good but declined later on - Gough, Wasim Akram, Saqlain Mushtaq. It's also fairly safe I think to say that Dharmasena would've been added to the Pollock, McGrath, Murali, Vettori category had he been allowed to continue his career.