5x5 and 3x5 are out of vogue for lots of reasons but it largely boils down to:

* Not enough volume

* Non-periodized

That first bit means different things at different phases of a lifting "career". But generally speaking "time under tension" and research into effective rep ranges has changed modern thinking on set sizes and volume.

These days people, including World's Strongest Men, tend to recommend higher rep ranges for beginners and those coming back to the gym to build work capacity and reduce risk of injury.

If you are just starting out all that matters is going in to the gym regularly and lifting some weight. 3x5, 5x5, or some complicated periodized program with a lot of accessories are all going to work.

That's why I recommend keeping it simple. Build the habit and build some strength. Once you've done that, you can get fancy if you find that you're really into it.

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.

3x5 like done by Starting Strength continues to work well for beginners looking for strength. After you tapped out the easy gains, you can use a periodized program for body building described by "the science" if you wish, but can do more useful weights because you are stronger.