That's sensible. A player's desire to modify Shadowheart's starting Dexterity is definitely analogous to wanting her to change into an automobile.
The original argument was about changing the starting class. Making Wyll not have any levels of Warlock, even though his quest is about his patron demon and his dialogue is about making a pact.
Changing Wyll into a Wizard is also not analogous to changing him into a vehicle with wheels, dude.
Both will be similarly removed from his dialogue and the overall game narrative. Though you are being autistic about my comedic exaggeration.
At any rate, minmaxing the PERFECT AMOUNT OF DEXTERITY for Shadowheart could've been done by editing files or console commands or mods, and didn't require the ability to change companions in a way that breaks their plot. The border is arbitrary too. I can change Frog to be a wizard, but I can't change her to be an elf? Why, changing her to a wizard already breaks all her dialogue, which is heavily based on her being a hotheaded fighter. Why can't I change her to be a dude, too? Plot is already broken by changing her class. Why can't I make her a naga with 6 hands, so she can sextuplewield great swrods? I could on the tabletop. And the plot is already broken anyway.
Its obviously a designer giving in to whiners. Its obviously not what they wanted. Its obviously not good, and would make the game less fun if you change starting classes of companions.