Electrical engineer: motors and sensors are not really any better- motors have gotten more efficient and sensors have gotten cheaper, but gold standard sensors like ring laser gyroscopes have existed since the 60s.

> Launch-thrust engines that throttle down low enough and preciesly enough for landing

In large part this is due to improved simulation- spaceX made their own software: https://www.youtube.com/watch?v=ozrvfRHvYHA&t=119s

Experimentation was also a large factor- pintle injectors have been around for a long time, but were not used in production rockets until SpaceX (who moved from a single pintle to an annular ring). Pintle injectors are very good for throttling.

> Better materials to handle stress for flip over manover etc without added weight

We're still using the same materials- good ol inconel and aluminum. However 3d printing has made a pretty big difference in engines.

More rockets use carbon fiber, but that isn't new exactly and the main parts are still the same variety of aluminum etc. Titanium has become more common, but is still pretty specialized- the increased availability was probably the biggest factor but improved cutting toolings (alloys and coatings) and tools (bigger, faster, less vibration) have also made a big difference.