I can understand a degree of frustration with hearing or seeing an idea or statement that you dissagree with but, your opening statement is factually incorrect. If everyone who said Shadowheart is the worst did not know how to play then very few people would make it to the "end" and fewer still would be able to make suggestions or offer opinions.
I would go so far as to argue that the feedback section would be of absolute null value if that were in fact the case.
Now while it is very true that I do not use Inflict wounds, I can easily defend that decision as at a glance and without prior understanding it poorly synergizes with her lacking mobility, poor attack rating (upon which the attack/save ratings are based) and limited spell slots particularly at the very beginning. In short it is not of immediately sound tactical value and therefore reasonable to disregard and easy to forget.
Now with regards to your other points regarding items, In the disclaimer I did mention that I would not be taking into account rare magical items such as the warped tiara of intellect and this extends to other items that are similarly easy to miss as building characters around said items typically requires prior knowledge of said things in advance.
Further on it should be noted that if a character requires specific items to be particularly good then it's the items that are good, not the character. Lae'zel can use prety much whatever you have on hand and will be able to handle pretty much whatever situation you encounter much the same with Astarion and Wyll.
Gale and Shadowheart both call for specialized setups.
I did also mention her having useful buffs and support skills and I stand by the notion that they are useful however, they are also hampered by concentration having a random arrow takedown that guidance you just applied make s a poor case for any of those abilities and her healing is completely negligible between resting and the slew of incredibly common healing items and foods there is very little need for a dedicated healer.
Now the reason I still rate gale higher than Shadowheart is quite simple, he has a slew of good, useful abilities that are not dependent on other characters setting him up. Grease creates difficult terrain and acts as a wide area firebomb near sources of ignition, Ice freezes blood and makes walking potentially complicated, he can put troublesome foes to freaking sleep and the list just goes on. As well as being able to learn every spell from whatever common random scrolls you happen to encounter. Beyond that, In case I have not driven this point home far enough misty step makes him VERY MOBILE which for positioning reasons is extremely valuable. If not for his poorly optimized stats and the fact that dying makes him a legitimate problem I'd rate him higher than Wyll for the sheer diversety of strategies that Gale can potentially bring to the squad vs Eldritch spam...
By all reasonable appearances Shadowheart is a unnecessary sub-par support character, OUTSIDE OF COMBAT I will note that she has other uses and values that are well worthy of consideration but that has little and less to do with what I am talking about here so the point about avoiding fights with her stealth skill is correct but irrelevant. Now she can be used to setup ambushes and whatnot but usually the parties basic stealth skills are more than sufficient to deal devastating opening maneuvers as noted by the chappel entrance where you can disable and kill over half of the enemy combatants before they can so much as take a move or in the case of dror razglin where you can easily remove a fair few targets from the fight before it even happens thus easing said fight. And this does not even call for Astarion.
Now as for my case for Astarion, I will say that his combat stealth skills, backstab damage, extra bonus actions, incredible mobility and minimal worry of any sort of repercussions make him a combat asset and general problem solver. And the value of all these things is immediately apparent.
Now as a final note: I'm not telling you or anyone else not to like the character and the fact that you have found a means of making them not only good but effective is pretty great and commendable even however, that does not change my opinion that compared to the others she could be better.
