Dentistry is not an exact science. Every individual and situation is different and you cannot just expect step 1..2..3 to always be the same. The experience related here is not unusual.
1. The decision as to whether the old filling should have been replaced depends upon the amount of remaining tooth structure, the status of the pulp, the allotted time that the dentist has and the patient’s cost preferences. (This may or may not have been clearly discussed before treatment started). The first temporary crown was not a custom-made, perfectly fitted crown and would have been cemented with a temporary type cement to allow removal at the next appointment. It is not unusual for this type crown to be dislodged by dental floss. It was simply placed to try to relieve discomfort and prevent further tooth loss.
2. At the second appointment, it may have been planned to complete the crown preparation, but upon removing the temporary crown, the filling also came out. This may or may not have been predictable. If the doctor was concerned about pulp vitality, he likely placed a sedative filling above the nerve and replaced the same or similar temporary crown. 2 weeks evaluation time is not unusual. And by 3D scan, do you mean an xray? An xray cannot determine the status of the pulp.
3. The tooth may have still been sensitive due to leaking margins from the temporary crown, but the dentist apparently determined that a root can treatment was not indicated. At this time I would guess that the tooth was prepared for the final crown and an impression was taken. A well-fitting acrylic temporary crown was fabricated directly on the tooth, and this would account for the “pushing and sanding”. The second person in the room would have been the dental assistant.
4. The doctor requested an evaluation in 2 weeks to ensure the pulp was ok (no sensitivity, no root canal required) before asking the lab to prepare the final crown.
5. This appointment I presume would be cementation of the final crown, whether the crown is semi-precious alloy, gold or porcelain. I would not recommend just leaving the temporary crown in place
6. I don’t see where a 6th appointment was needed, except a follow-up check.