The film strength of Mobil 1 is virtually identical the film strength of mineral oil, so I doubt if it was film strength issue. The higher grade synthetics have very high film strengths, but that probably wouldn't have helped in your case.
I think your problem was not the film strength it was difference in viscosity, the identical 50 rating notwithstanding.
Synthetic oils withstand higher temperatures before breaking down, and have more base stock and less viscosity modifiers. Synthetics wear out, become acidic, and eventually become saturated with suspended soot particles, just like regular oil.
Synthetic oil was originally developed for high performance racing engines. Mobil tried to popularize synthetic oil for passenger vehicles back in the early 1970's. At the time, Mobil was promoting 20K or 25K oil changes with synthetic, but they soon backed down from this. Synthetic oil is a good choice if you have a vehicle with a high performance engine (in fact synthetic is required for many of these engines). It is also a good choice if your vehicle is operated in extremely cold climates. It has higher resistance to breakdown caused by heat and it flows better in extreme cold.
Unfortunately for the synthetic oil industry there is virtually no advantage to using synthetic oil in a non-high performance engine that is operated in moderate climates. Synthetic may give you the peace of mind of knowing that you are using an oil that is better than necessary for your vehicle, but it won't reduce wear or extend the life of the engine. The mistake some people make it to wrongly extrapolate these benefits onto normal engines operated in mild climates, with the ultimate lack of any knowledge being manifested with statements such as "synthetics provide 'Peace of Mind,' or 'Cheap Insurance,'" or other such nonsense.