The fact that felons are barred from the RKBA does not undermine the right itself. Felons were historically all subject to the death penalty (except IIRC mayhem, which was punished by public dismemberment that might not technically kill you). Every felony was punished by death. Later that was modified to permit "transport" to the colonies--essentially banishment. Over the past centuries the laws have been modernized and relaxed so that only murder carries death, and other felonies have a mix of conditions. But what remains is the notion that once you are a felon, you have lost a number of key rights and may never get them back. Whether that's an improvement over being hanged is debatable, but it is well-established. The founders would not be surprised that felons lost the right to vote or bear arms. They would be surprised that so few felonies were subject to the death penalty. A return to the old way would curtail the ever-expanding list of felonies.
Well it would depend on the crime that the felon committed for the "kind of" surprise of the FF.
In many cases, where theft, or violence was the crime, I agree the FF would be surprised that the felon retained his right to life. However in other cases, the FF might be surprised that the unconstitutional behavior of the Government led to that person being marked as a felon.
Indeed as Justice Brown said in Bannon ""The word felony was used at common law to denote offenses which occasioned a forfeiture of the lands or goods of the offender, to which capital or other punishment might be superadded according to the degree of guilt.". Do all felonies pass scrutiny of this definition, are all felonies potentially capital offenses?
By barring felons, then it opens a class of people who are citizens who can have their rights restricted, and it's socially acceptable to boot. This gives government the opportunity and the means to restrict rights of others by reclassifying them as felons. At the end of the day Government defines who felons are, by agreeing that the government has the power to restrict rights of those so defined, this opens the door to some pretty serious potential for abuse.
As I mentioned in my post
above, every American commits on average three federal felonies per day. Just because most of the time people aren't charged and convicted doesn't mean that these did not occur, and as we all know ignorance is no defense.
In the words of Ayn Rand
“There’s no way to rule innocent men.
The only power government has is the power to crack down on criminals.
Well, when there aren’t enough criminals, one makes them.
One declares so many things to be a crime that it becomes impossible for men to live without breaking laws.”
YMMV