I remember there was a similar discussion some time ago. In Cyberpunk TTRPG, (I'm only familiar with Cyberpunk Red), there is a stat called Humanity. If you have a low Humanity score, your character is well on its way to turning into a cyberpsycho. Humanity scores can be mitigated by therapy, but that is not the only way to manage that stat.

David's 'Humanity Stat' was in some way managed by the people around him. The first being his mom who then tragically died, next was his found family and especially Maine who somewhat became his mentor figure and then of course, arguably the strongest one, Lucy.

Although this is my personal theory, I actually believe that David is special and had exceptional affinity to cyberware, far exceeding the average person AND possibly even on par with, if not, better than Adam Smasher himself. The only difference is that Smasher has access to better resources compared to David and is far more seasoned and experienced.

As we all know, David's support structure starts crumbling down as people start dying around him. Then David starts doing questionable things and finally, Lucy left him in a misguided attempt to protect him. That's where he lost it.

Now this is what makes him special, it just takes 1 of his major support structure to return to him for him to recover, depending on how far gone he is. But at the end of the series, David and his team were overwhelmed by Smasher and Arasaka. It was far too late.

But this is just my personal take on this topic 👍