Forecasting labour needs - an activity that I have been professionally involved with in the past - is little more than mysticism. The only thing you can know with anything like accuracy is the retirement (NOT the resignation) rate of the current workforce.
Every other variable is just a guess based on assumptions you can never be confident about. The two assumptions governing the current predictions are about retirements and demand growth.
The real question is 'are there enough people in the world who have the necessary skills and abilities to become pilots?' The answer is clearly 'yes', so everything else comes down to whether the industry can make the job attractive enough to recruit the numbers they need. The airlines are under such cost and competitive pressures right now that managers are psychologically incapable of confronting this issue. So they resort to making the same noises as their aeroplanes (whining).