I think the shooting took place in Chicago, or was it Milwaukee."
I stand corrected -- the October 14, 1912 incident was in Milwaukee, not Buffalo, and was very equivalent to the Trump shooting near Butler, PA.
One difference is that Teddy Roosevelt carried that non-fatal bullet in his chest the rest of his life.
As for some of the other presidents, I agree that not all threats were equally serious.
You noted one unserious threat against Obama, and we could add to that the vehicle crash against Biden's White House, which posed no serious danger.
Squeaky Fromme after 1975 assassination attempt:
On the other hand, in Pres. Ford was also unhurt in 1975, but avoided death in Sacramento from a shooting by Charles Manson follower "Squeaky" Fromme, only because her gun failed to fire.
Then again, two weeks later Sara Jane Moore fired and missed at Ford in San Francisco, though wounding a bystander.
I'd call those very serious even though Ford was unhurt.
As for the shooting of Trump and others in Butler, PA, I'm hopeful we'll get an honest investigation, but would not really expect one until after Republicans take over in January 2025.