In this case it matters less what the founders intended and more what the framers of the 14th Amendment thought almost 100 years later. You can read in Richardson v Ramirez a bit of a history of felon disenfranchisement; a reasonable summary might be: "there was a lot of haggling over the specific language of the clauses of 14A, but disenfranchisement for crimes was a consistent point of agreement".

Of course, that doesn't mean that it's right to disenfranchise felons (it almost certainly isn't), nor does it mean any state is obligated to disenfranchise (most states don't). It does however mean that it's not straightforward to appeal to the Constitution in arguing to get rid of it.

At the time of the Founding, most (or all?) felonies were punishable by death; I suspect that they would have considered release from prison with disenfrachisement to be quite merciful.

I could see probation and/or a required (and taxpayer funded) civics education course as part of a conviction; but I agree. Either the civil restitution and rehabilitation (I can dream we'll be a first world nation someday) are completed by the sentencing or the sentencing is insufficient and should be fixed in the law.

Permanent dis-enfranchisement is a way of ensuring someone remains ostracized from society and is forever given reason to work against it.

They were fine with depriving women and black people the right. I wouldn't expect them to have been super progressive on felons, either.