Weird. I've lifted on and off for 25 years. For most of that time I did the stereotypical 3x8-12 and saw much slower progression. During the past couple years I switched to a 5x5 plan and saw massive gains in strength, even while I was cutting weight via a caloric deficit (was eating 1500-1600 calories a day, but had lots of protein and adequate carbs).

For reference, I went from a dumbbell bench press of 45lb to 75lb in 4.5 months (5x5). Previously my progress was much slower.

I'll caveat that I've obviously not closely controlled for all factors and I'm an n of 1. Additionally my interest is in having a great strength to weight ratio, rather than being a body builder. I'm a climber and that's an important consideration.

It's not that weird; Stronglifts (SL aka 5x5) and Starting Strength (SS aka 3x5) both utilize progressive overload to stimulate gains.

Progressive overload works. Those programs "work".

They are just out of vogue for beginners, and they are both targeted towards beginners.

I'm sorry but what?

You have been lifting weights somewhat regularly for 25 years, majority 3x8-12, and the switch to 5x5 increased your dumb bell bench press from ~20kg to ~35kg?

There is just no way. That is extremely light weight. Like, most beginners who follow any sort of progressive overloading system will be at that level in 4 weeks starting from essentially 0