Hello You have very well explained what all treatment is going for you and by reading this I can only say one thing that whatever treatment the doctor has decided is based on the clinical examination and what is best for you. Sometimes to rehabilitate good functional teeth in your mouth some judgements have to be taken wherein the healthy teeth have to be treated. This is also a good treatment do not worry about the life of the root canal treated teeth, they are going to stay long as long as you are maintaining the oral hygiene very well. You have to be very careful and very active when it comes to oral hygiene. Just make a visit every six months to your dentist so that any other tooth doesn’t go to the stage of extraction