Working for somebody doesn’t mean that you have to agree with him/her all the time. Don’t be afraid of arguments when discussing about the path a project should go musically.
Many directors/producers I met prefer a composer who has a strong own opinion on what the music should do over a composer who just says “yes”. Even if your client seems intimidating doesn’t mean that you should not express your point of view. Not just because from such things sometimes the best ideas might arise but also because it is psychologically way healthier. If you keep working on things where you just say yes but don’t really agree you will eventually begin to feel really frustrated. So while harmony and agreement is something that feels better at the moment, sometimes a professional and constructive debate can be a very strong creative spark.
Of course, the same rules and principles apply here as they do with any respectful discussion in life. It is all about compromises and you should stay within reason regarding the intensity of arguments. If you feel like you’re fundamentally disagreeing about a point without the chance of a compromise in between, it will not help to poisen the working atmosphere by fighting over this. In such cases, usually the client wins and you should find out yourself whether you can still work with this or need to move along.