The 5 is a very smooth engine. a power pulse every 72 degrees.

Auto makers would have built 5s, but they could not machine a proper 5 cylinder crank shaft.

More makers have used 5s than you might think. Mercedes Benz produced the first when hey needed more power than their 4 but did not want to engineer a new engine.

The power figure that you cite is almost exactly what our '96 855R had.

The engine model numbers like T5 may not correspond to the number of cylinders. I do not know when they changed.

Currently Volvo T4, T5, T6, and T8 engines are all 2.0 liter, 4 cylinder engines.

I doubt that there is any relationship between the older V6 and the modern V6.