Rangers will never catch up for years, their financials won’t allow them to compete with Celtic. Celtic will win the next 10 titles minimum
If Rangers can snag a year few years in Europe, they'll get the finances to compete pronto. As it is, they just need one or two big investors and they'll catch up to Celtic now. Besides, Rangers showed this morning that the gap isn't as bag as what it's thought to be. More consistency and better players in a few positions and they'll match them on the field without the bigger finances.
I think Rangers will be primed to compete within 3-4 years if things go well.