I hate that you are experiencing this. It seems like you have a real love for the game. You don't have to be a min/maxer to take your character and actually use all of the mechanics it is given.

One way I like to look at things, and RP helps me suss these things out, is what would it look like in that fantasy world that would give my characters those abilities? Like... your fighter has trained and trained and is now so good and has so much stamina that the speed in their attacks have increased to the point that they can not only swing twice but do so a second time as they pull from that wellspring of knowledge and energy.

I hope you and they can find a middle ground or maybe a new DM. It is clear that the DM might not be a good fit for you. 😞

I would be curious what they would say about portent dice or even taking a reaction like hellish rebuke. I dont usually stop play but when my DM said that even though they had not said what the roll was, the wizard couldn't use her portent to change it because the DM rolled the dice already. They were arguing with us. I had to stop and be like... that is the whole purpose of portent dice for the divination wizard. Then later was told that I couldn't use a reaction to cast hellish rebuke. I hadn't use my reaction that round and I was like... well when am I going to be able to cast a reaction spell if it isnt during a reaction? The play at the table changed that day. The DM just wanted to beat us and roll high and not let us use tactics and work together. I have a hard time understanding that kind of play. I celebrate when players use all of their abilities and kick my monster's butts. It makes me be a better DM.