I have a metric ton of 5e experience and CRPG experience.
Honestly the level of difficulty is in a decent sweet spot right now....if you know the rules, mechanics, and certain abuses (Wizards learning Healing Word, the power of gaining Advantage with GWM).
In 5e, Action Economy is king. That means the side that wins tends to be the side that can take more Actions. You're almost always outnumbered, so the enemy has more Actions by default than you. So how do you make that easier?
Summons. Absolutely everyone should have some sort of summon, even if it's just a Find Familiar spell. Raven Blindness is amazing and broken AF. Spammable zero cost Blindness spell with a huge movement ability? Yup. Much more importantly, every attack against your summon is one less attack against you. My Giant Spider from my Beast Master Ranger has something like 39 health, which is more than anyone in my party even at level 4.
Any spell or ability that causes the enemy to waste their Action is the name of the game. The Giant Spider's Web attack to cause the Enwebbed effect (really just Restrained by the rules of 5e) is a perfect example of this. I am trading the Action of my Giant Spider, for the Action of the enemy. My spider *could* cause like 4 damage....or it can make an enemy waste their turn instead of doing 20+ damage. It also provides instant Advantage to the rest of my party, which is the second tip...
In 5e, party synergy is Queen. One party member granting Advantage on a target to the rest of the party is critical. That means Sneak Attack for the Rogue, much higher hit chance for the GWM Fighter, and an almost guaranteed hit from the Warlock with Agonizing Blast + Hex. The corollary to this is denying your enemy synergy. A target has a bunch of armor + a shield? Don't waste your time with Attack spells/abilities. Start hitting them with Status effects like Frightened and Save spells like Shatter.
All that said, I am glad about the level of difficulty. I want a spiritual successor to BG, not DoS 3 the D&D DLC. This isn't me trying to gatekeep. I slogged through BG 2 not having a clue how any of the rules worked, often having to lower the difficulty. Based on Larian's previous EA work, this is approximately the "Hard" difficulty for the eventual released game. So having a hard time is to be expected.