I use the word "irritating" about the lack of custom party options, but I still think this is a great game. If I thought Larian would never add them, I'd just go ahead and start Act 2 and I'm sure I would enjoy it. I'm just holding out hope that it's still something that will happen, though I was disappointed it didn't make the cut for the most recent patch.
They also really need to fix the unpopular races. All of the popular races have a niche, like Wood Elf if you want to move faster, Human if you want a Shield, Wood Half-Elf if you want a bit of both, and the abilities of Drow, High Half-Elves, High Elves, Tieflings, and Half-Orcs all have things that you can stack up against what a Wood Elf gets and there are some pretty decent builds. You can just match up the unpopular races with various classes to see they clearly get less. With Dwarves, it's glaring because the Shield Dwarf just gets less than Hill Dwarf if you choose a class that has Medium or Heavy Armor, but all of them lost something in translation from 5e to BG3 that just wasn't replaced. That's bad game design. They should have said "Why would I choose to play a Rock Gnome instead of a Wood Elf?" Then made sure it fit somewhere. Like give a Rock Gnome Expertise in Sleight of Hand (to replace the Tinker ability they lost) and suddenly, without being OP, you might choose a party with no Bard or Rogue but has a Gnome (of any class) who can still competently do the lockpicking and trap disarming; i.e., a niche. And make Gnomes the "expert class" by giving Forest Gnomes Expertise in Handle Animal and Deep Gnomes Expertise in Stealth. Then you'll always feel like you have a reason to play a Gnome, even though they are slow. You could easily make Halflings "just interesting enough" by giving them Stealth Proficiency; it won't always be a no-brainer to take Wood Elf instead of Halfling, even though they are faster, and you could go Lightfoot for a lot of Stealth or Braveheart for just enough. If you just give Githyanki exactly what they had as racial abilities in 5e (specifically, the same as they are now + Psionic Resistance), they will be no less compelling a choice than they already are in 5e. And Dwarves are easy to fix, too; just give all Dwarves Light Armor Proficiency and Shield Dwarves get one better Armor Proficiency than everyone else (e.g., Medium + Shield (duh, it's right in their subrace name) if their class only has Light or No Armor, Heavy Armor if their class has Medium, and Heavy Armor Master if their class has Heavy Armor); then Dwarves have a "niche," which would be toughness for Hill Dwarf and armor for Shield Dwarf.
Once they fix the unpopular races with a minor feat here or there, they will truly have a game where a custom party is fun, assuming we eventually get a custom party.