What did people ride for cold weather cycling "back in the day?" (Is it cheap?)
Wool, wool, and wool. Wool undergarments. Wool over garments. (Maybe tweed as well.) Wool is a amazing material. It tends to perform better than synthetics (although the gap is closing) for keeping you warm when it is wet and cold outside.

On descents people also used to just either tough it out or did life hacks such as putting newspaper down the front of the jersey rather than rely on fancy rain shells.

Now here is the caveat about wool and the old world approach. Real wool garments are often much more expensive than equivalent synthetic garments. So from this perspective synthetics are a much better choice than killer cotton if you cannot afford wool. Synthetics also tend to wear a bit harder and typically don't need to be hand washed, so wool is more care. You typically only had a few garments which you washed by hand at night before the next day of riding. You also had to learn how to darn wool, so you could fix damage that can happen to wool over time.

Synthetics dominate today because of the cost, reduced care and good enough performance.