I agree with this statement with a slight modification: "until unless you work with some competent engineers and challenge yourself with technical problems on bigger projects" which challenge your pre-existing pool of knowledge.
But that statement covers the development of competency of individual. In order to land a job which pays well, this is not enough at all.
The MS degree has a huge advantage. A MS degree from a university of good standing in US, UK, Canada, AUS, New Zealand makes it easier for you to acquire a job at a company of international repute, and you are paid much better than the others as well.
In Gulf, one will routinely come across adds which requires that the applicant must be registered as professional structural engineer (like CEng, MIStructE) in an internationally recognized regulatory authority (mostly UK). These are the people which pay almost twice to the people that satisfy their requirement. The requirement is simple, they pay to the privileged ones. This criteria of hiring anyone who is registered with a particular organization ( mostly Institute of Structural Engineers, UK) gives undue advantage; but, it is convenient for recruiters. In most cases, the one who is registered with Institute of Structural Engineers, would have got his Masters from there as well.
Any one who has got the job (especially in Structural engineering) in western firms based in Gulf without the MS from above mentioned countries, count your self extremely lucky.