As everyone is different and all doctors are different I'll just tell you my story....

I have occular MG - woke up with double vision one day - after seeing my neuro she recognized it right away and started me on mestinon - BUT sent me to the greatest specialist for MG in Canada because she knew that he would be the one to see for the most up to date info etc etc -
He put me on pred AND imuran - weaned me off mestinon - the reason he put me on pred was because imuran can take up to a year to kick in - so he gave me the pred so I would have relief sooner.... I was on pred for 9 months (weaned off etc. etc. during that time - and a lower dose)..... I am now on just imuran and "knock on wood" all is well. Come spring he will start to bring my imuran dosage down to see if I can tolerate a lower dosage. I only carry mestinon with me in case of an emergency - I've never needed to use it so far.

So, to answer your question (long story LOL) I would say with my experience NO mestinon alone didn't work for me (and I was on just it alone for 6 months)