I have a question tough, what with pilots who get their IR or CPL in the USA like in Arizona, and have never fly in a cloud... ?
Does that makes them practical capable of flying into heavy IMC ?
Yes.
IR training, whether FAA or JAA, is almost entirely done in VMC, with the LH pilot's vision being obscured with some device. So he can't see out anyway.
Another thing is that IR training is very very hard. Most of mine (FAA IR) was on partial panel (AI & DI covered up so only the TC, airspeed & doing timed turns with the compass), flying approach after approach down to minima, no enroute segment to have a rest, weeks of utter exhaustion. In practice, one would be flying a well equipped plane, with an autopilot, and if one got a real emergency (and a loss of most of your instrument is an emergency) one would not create extra work for oneself. A well equipped plane makes a huge difference and all serious IFR pilots have one.
Another thing is that when IFR one rarely flies in cloud. The enroute section is VMC on top. If it wasn't, you will generally collect ice because Eurocontrol airway MEAs usually place you above the 0C isotherm. One spends a lot more time in cloud flying "VFR"
around the UK than when flying airways. On my last long trip, about 30hrs IFR, I logged less than 5 mins instrument time.
In the long run, your original training fades into the distance and you are only as good as your last flight
That's why the FAA IR rolling currency is a good thing - you have to do 6 approaches in the last 6 months. The US safety record is good.