Flying for a living is nothing to do with flying. I haven’t a clue about the CTC selection process but I also would strongly consider my suitability for flying if I failed an extrance selection twice. Even though flying the real thing might be easier than flying through boxes, the main point has been missed. When you are fying for a living have to be able to fly almost without thinking. You must be able to put the aircraft exactly exactly where you want it. By doing so, it will give you the spare capacity to think. Are you where you should be? How long will it be before you get you your next waypint, turn etc. How long can you hold for? If Plan A goes to worms, his much fuel will be required for Plan B or C? How can I sell that to my colleagues? The aircraft might be able to do some of that work for you, but do you trust it? You have to have some rough figures in your head to check the correct guff has been beaten into the magic box. When you are doing this is bumpy clouds at night you don’t want the overhead of the effort put into your flying to be too onerous.
Lastly, there is nothing worse than flying with those who think they are the “Ace of the Base” or gifted flyers. You want to be flying with Mr or Miss Average. They are easier to work with.
So as Wiggy said, you will be investing a considerable amount of money and time if you wish to (try and) obtain a commercial licence. Make sure it’s not wasted investment.