Advantage and disadvantage are able to cancel out in BG3. So if your enemy is on high ground, applying truestrike would negate the attacking disadvantage effect. It also stacks, so if your enemy is on highground with Blur, applying truestrike alone will not remove your attacking disadvantage. I wouldn't say Larian's system removes the value of the X amount of spells, but means for them to be used differently. If you are to hover over your roll in the combat log, it will tell you if your attack had advantage/disadvantage effects calculated or negated.
Not too sure how this fits but you may have some insight - my level 4 Shadowheart using a shield was able to reach 19 AC standard. Shield of Faith bumped to 21. Even at 21 AC, I'd still get trucked if I didn't observe enemy advantage or impose disadvantage, simply because of the modifiers. A lot of the things we have the potential to fight have huge modifiers to their attack rolls (+4 and +5s), and if no huge modifier, vastly superior numbers. Having my 21 AC cleric trashed in one turn by trip attack, multi-attack, action surge'd melee inspires me to use the abilities you said were ruined, on top of the looming pressure that the rest of my party could share the same fate. If anything, I'd say make the AI also attempt flanking, as they already run for highground (if ranged). I'd go as far to say that in the EA, advantage/disadvantage is far more costly if not mitigated with the spells you mentioned. Claiming advantage/disadvantage by height and positionging turns the game into "king of the hill" is almost like saying you don't know how to break a line of sight and don't know how to judge ranges.
There is also the presented issue of attempting to run around an NPC for that backstab. If you're not meticulous, you're more than likely to trigger an attack of opportunity with your side exposed - I have definitely died from not being meticulous in my positioning. The counter would be, "just jump" and I personally believe there should be an acrobatics check if jumping out of an attack of opportunity - maybe it hasn't been implemented yet.
Maybe if we started out killing rats, the system's general progression of AC and spell availability would make sense, but we're not. We're asked to go find a druid in the middle of a giant goblin warband, lead by netherese infused fanatics. Have to keep in mind, WotC is working WITH Larian - so whatever the finished product is, they signed off on it.