You can't really compare today to the reopening phase. Not only has park attendance significantly increased but standby lines cruised during those months. There wasn't a huge incentive to cheat when the standby lines (for the most part) were quick. So you have 1) more people in the park, 2) a financial and time incentive to cheat and 3) I don't think the majority of the people at the park during the reopening phase knew that DAS was a thing. Since that period, DAS has been well advertised - whether that is by formal announcements from Disney explaining the new system and the two extra LL's reserved in advance or by word of mouth/social media. I used to listen to the WDW prep podcast but had to stop because for the past year, almost every single trip report has been a DAS group. It's hard to relate or gather tips from a group that has the ability to maximize their time to that extent. Maybe I have a less rosy picture of humanity, but in general I think you're going to experience a lot of poorly behaved individuals in Disney World because they've spent a ton of money.
Regarding the increase of abuse of DAS if a Doctor's note was an option....how would abuse be any higher than it is now? Right now you just have to open your mouth and speak words.
My family was at Hollywood Studios in November and made the mistake of getting in the Minnie Mouse meet line (Red Carpet Dreams) because it was advertised as 50 minutes and there was no LL offered so I assumed it would move quickly. In actuality, it was a 75 minute wait where the children waiting in line sat on the concrete for 10 minutes at a time because the line did not move. As soon as we arrived to the queue, the first DAS group showed up and moved straight to the front. And after that, it was a steady stream (and they've waited 40 minutes because the posted wait time remained 50 minutes the entire time). We finally go to the front of the queue and the cast member asked us the number in our party...when another adult DAS group showed up and got right in front of us. At that point, my 8 year old started crying because she's had to sit there and feel like no matter how long she waits, she's never going to get her turn. Your welcome to think my child is a brat (I don't care) but it is difficult for a young child to understand why she's not getting her chance because a steady stream of adults with invisible disabilities get to go first. It definitely woke me up to realize how many DAS users are in the park.