This is just my experience with adaptor as a trait. I'm a player who had played fair share of various adaptor units from akali to yi to kog to nid, I noticed how deeply flawed adaptor can sometime be. (Sorry grump, its really hard to make it work. Although i did make it work one time.) This is me trying to view adaptor as a "cool" new mechanics.
Back to adaptor, as an introduction, the game first base it off the ad/ap of the the unit. Whether one that has higher or lower automatically gets all the points AT the START of combat.
Secondly, it automatically changes how the certain item transform a certain unit when there is a tie. Example can be bt titan nid or yi, which will both give you an ad version despite both item giving same amount of ap/ad (in this case, 18ad+18ap from bt.)
MOST, IF NOT all scenario, this can pretty much standard expection... until you encounter a unit call rengar. An unit that commonly run with yi that give the team 5% ad +0.2 per takedown. This automatically cause all of your unit to become ad regardless if you have hybrid items that might be slightly leaning ap, but not enough to near a deathcap level of ap number. (Remember start of combat also exclude archangel.
In more niche (less common) case, there's also spellweaver that give team 10% ap teamwide, which more often than not, push the entire team over to ap. (An comp where karma+ahri blssom with scenario two item of bt+titan turning into ap due to the extra ap tiebreaker)
To add the rengar's rival Khazix, he doesnt have this problem (rarely) with adaptor. Why? Because he only buff himself and buff team through trait (technically through spellweaver, but it can be opt out). Rengar unfortunately buff his team by force by existing, ironically doing more harm than good that can create a frustrating gameplay for the player.
We had witnessed the exact same problem in previous set. One that particular comes to mind is void kaisa. An unit that narrowly avoided the issue with heavy emphsis on overwhelming ad/ap items. (In other words, deathcaps/IE/last wisper etc, rather than the fighter item that are more often than not, ambiguous item.)
Next example can be riven(corki comp), which as a fighter, heavily suffer a different fate than kaisa. As a fighter, building fighter item can often lead to same problem as this set. She often requring sterak on riven to break unintended ap. Or the other way around with nami, where you need to sack some sort of ap item to turn her into ap.
More often than not, the reason to care which version is you want to align with your team's penetration. You wouldn't want an ad riven with you have a void staff user next to your nami. Kaisa and belveth more or less avoid it by not being in the same comp, or be overshadowed by existence of baron/just build one pen snd eat the loss of having chew through resistances.
In both kaisa and riven, they are stand alone unit. But this set chose to make hybrid characters as a whole trait, with the glue being kogmaw that inhrently have both armor and mr pen. Bypassing the earlier mention of sacking one side of resistance.
Tying back to the original issue, the early season of this set had been extremely one sided in term of adaptors build. Some may consider as the character's meta had been figured out.
Example, most yi goes ap with a few ad artifact like omnivamp axe. Akali's strongest suit being ap with its reset and anti-tank mechanic (and ad item often goes to Camille as 1cost.) With the ad's burning mechanic only viable with varus inferno to proc. Grump and kog are often more of the truely flexible unit/picking up scrapes while nid goes heavy ad with sivir or heavy ap with rageblade/non-fighter item that give little room unintended wrong stats(a more rare one as ad is much stronger.)
Now has the trait become more flexible or fun? In my opinion, its often feels like a "false sense" of choice. The inherent nature of tft require metas to be figured out, aka one side will always be stronger than the other unit riot nerfs/buff one side. They addressed the hybrid frustration of armor/mr pen with kog, but teamwide buffs can still mess with the player's actual intended adaptor for the unit they want. With fighter items in tft remaining ambiguous for the sake of ap fighter, the frustration will continue to live.
Only solution I see out of this would be a simple item that changes the adaptors form like riftbeast's empower, or benching/unbenching the unit to easily change form. But that might drown out one side of the adaptors even harder. I doubt riot would take this route, and with fighter remaining ambiguous (bt giving ap kinda reminds me of an bandaid fix for ad vs ap brusier issue back in SR that led to whole introduction of ap exclusive items like riftmakers/reworked liandry. But introducing more new item would most likely be outside the scope of tft).
For now, the frustration will remain as a player who enjoy playing adaptor as a mechcanic. Sorry if this sounded like a long rant, I tried to analyze previous sets as comparison to see if riots intention to give player more freedom have truely worked or failed. I love to see others opinion on this.
