Saigon fell in a very similar way. We left the people in that city to the mercy of the Cong and many paid with their lives. I'm probably a great deal older than you so I remember that vividly.
My issue with any President taking military action is that very few have actually served in a combat situation since Kennedy. There's a certain level of troop morale that is destroyed when a mission isn't completed.
Should we be in other parts of the world taking care of weak militaries run by other countries? I personally don't think so but I also understand the consequences if we don't.
Vietnam was a long war. I lost numerous friends in combat as well as seven who passed after returning from the effects of agent orange or worse, suicide. We've been in Afghanistan for twenty years and we did indeed have the Taliban under control and in fear of our forces. Now I ask, for what? The men and women who died there died in vain.
No right answers to these questions, only opinions but again, I agree with you that each President for the last twenty years owns a piece of this. Biden will forever be know as the President who bailed out on the mission before it was complete.