The original 1962 missal's changes can be broken down into 3 categories:
1. Making the 1955 Holy Week changes permanent.
2. Updating the calendar of saints and streamlining the ranking of feasts
3. Changes to the actual Mass? (this is debatable. See below).
People can yell and scream all they want about pts 1 and 2 but there's nothing inherently unorthodox or heretical about these changes. Were these changes perfect? No. Are they set in stone? No, so when we get an orthodox pope, he can edit/delete this mess for the future. No problem.
The only problem you can raise about the 1962 missal is with the changes to the Mass itself...a) inclusion of St Joseph in the canon, b) removal of the 2nd confiteor, c) maybe some other minor changes.
However, the ORIGINAL/1st edition of the 1962 missal (the one approved directly by Pope John23) did NOT add St Joseph to the canon (this was added in later editions). So if +ABL used the 1962 missal without St Joseph, then there's no problem there.
I'm not sure which edition removed the 2nd confiteor but +ABL added that back in, so no problem.
So really the use of the 1962 missal by +ABL can only be criticized for the Holy Week changes and the Calendar updates. I really think this is small potatoes. Pope Pius XII ordered these changes to occur (it takes years to update a calendar, so this work was started long before Pope John was pope). Even Fr Wathen said that these changes are minor and though not perfect, don't pose a big issue.