The biggest problem with the space shuttle wasn't tiles or tanks or SRBs or O-rings. Or even needing to practically rebuild it between flights.
The biggest problem was that the first four orbiters should just have been the Mk-I model. All those things that were found to be problems in the Mk-I model should have been improved or even fixed in the MK-II and subsequent orbiters.
Yes, they made improvements in the later orbiters based on early experiences with the Columbia, and fixed the O rings after the Challenger accident, but there never was a truly improved model.