The Red States have been ignoring the old Supreme Court rulings.

Citation needed. Regardless if states follow the rulings, the supreme court can shift the views of the nation. After 2015 same sex marriage ruling, there was much higher support for same sex marriage, with noticable large increases with Republicans corresponding to the Supreme Court ruling:

https://www.pewresearch.org/politics/2017/06/26/support-for-same-sex-marriage-grows-even-among-groups-that-had-been-skeptical/

From the Article from 2017:

For the first time, a majority of Republicans and Republican-leaning independents do not oppose allowing gays and lesbians to marry legally.

To your other point:

myth that there would be substantive change if we just kept Biden in office.

When Biden assumed office, we were in the middle of a global pandemic, still social distancing because there were no vaccines, and we're having a 9/11 worth of American deaths every day. Maybe returning to normal life wasn't substantive for you, but there have been huge changes over the last 3.5 years of the Biden presidency.

Because he's either powerless, in which case so would Trump be, or he's willfully allowing this, in which case the worst case scenario is already playing out.

In this situation, do you think Trump would be willingly allowing atrocities or actively driving and enabling them? A Trump presidency would clearly be the worst case scenario here.

EDIT: just formatting