So to begin with, I haven't yet gotten around to playing 5e, and as such have also not played the module that you're talking about. The spell selection that you describe sounds very wisely-crafted from my experience with other editions, especially in the absence of a party face. I'll rely on the wisdom of the other answers to discuss your specific optimization.
So for a more general perspective: different tables see different encounters. So the first thing to observe is that what's reasonably optimized for the kinds of situations that one party gets itself into may be poorly optimized for the kinds of situations that another party gets itself into. It may be that they expect the situations that you get into to go a specific way that their games always go. They may not have a party face because they may not expect to need a party face. They may not see the value in Shield because they may expect the mage to never be targeted. They may not understand why you'd want to charm someone outside of combat, because 'outside of combat' may be equivalent to 'during cutscenes' at this table.
If this is their perspective, then they are probably wrong in this case, as I understand that many modules tend toward requiring a variety of skill sets from the characters.
Furthermore, different tables also have different optimization expectations, even if everyone agrees on what the expected encounters will be like. I think that this is less likely to be the case if you're working out of a module, but some games will prefer interesting and well-rounded characters - maybe no one can hit that DC 25 at level 1 even on a natural 20, but all of the characters feel believable and lifelike and are rich individuals. A highly optimized character in a game like this could overwhelm every mechanical challenge and trivialize the worse-optimized characters. On the other hand, in a party with a high expectation of optimization, one weak link breaks the chain. If they need the proverbial Batman wizard, able to do all kinds of things at a high level of effectiveness, and they instead get a sorcerer who can do his small number of very important things very well and very frequently, there are going to be weaknesses that the party might struggle to overcome. This does not sound like it's factually the case here, as it sounds like your character is more optimized than the rest of the party, and like the rest of the party is complaining about a perceived lack of optimization on the part of your character, but it bears mentioning that this may be where they're coming from and understanding their perspective will help you discuss the topic.
It may also be that their DM tailors challenges to their skill set - as a good DM should do - and since they've never had this kind of skill set, this kind of skill set has never been tested. This is also something to consider, will the changes that the DM makes to the encounters make the game less fun for the other players? Or, more accurately, are the other players afraid that the changes that the DM makes to the encounters will make the game less fun for them? This is probably a question for the DM, not the other players.
On that note - talk to your DM! If he's played with these players before, he's likely to understand where they're coming from, and be able to answer your questions without getting upset. Once you more fully understand where they're coming from, you're much more equipped to address their concerns.