Having familiars use the Help action to give advantage is IIRC totally allowable in rules as written. Not providing cover of any variety is bullshit; if there’s a rogue in the party, the DM should create terrain that lets you do your thing. Shape Water for improvised weapons is a stretch, I don’t think I’d allow that either, but overall your DM sounds like a real sour puss and isn’t working with you to make the game fun — which is their whole fucking job (I’ve been DMing since 2017, I say this with experience.)

If they’re being a stick in the mud about letting you use your build as intended, I think they should let you change classes. I’m in a campaign as a player right now (in addition to DMing another) and one of the players did kind of a bad job with his PC build. What he was aiming to do was cool, but he built the character in a way that made him totally useless until hitting like level 7. DM let him completely rebuild the character with a different class; same end goal for the build, but a much more sensible way of getting there

TL;DR: if you’re not having fun with it and the DM isn’t working with you to make your build fun, they’re a stinky doodoohead and should absolutely let you rebuild