Right now there's no chance that Saudi Pro League would be as competitive as any of the top leagues in Europe. Quite rightly they are alluring players from Europe, but most of them are either old and past their peak, or they aren't just good enough players, mind you that the Saudi Pro league is yet to allure a world class player that is in his prime.
Having said that, remember that what the Saudi's are trying to do right now is somewhat similar to what the Chinese Super league did a couple of years ago, but we all saw how it ended, i wouldn't rule it out to end the same way for the Saudi's.
I agree with your assumptions, but if they never try then surely the Arab Pro League will remain stagnant or maybe drop lower than other countries' leagues. The scenario is the same, of course China and Saudi are trying to improve both in terms of business and increasing the quality of competition, but the result depends on management and how the team there adjusts.
Without a large income, this step will stop because no investor wants to continue to lose money every year. I can't say anything about the future of the Arab Pro League, but so far they have been brave enough to tell the world they want to develop.