Question po: if preamps would output 1-2V, do you still need one considering new players cater the same gain level?
Don't forget about impedance matching. Gain level isn't the only thing that matters.
Just because an amp's input section was redesigned to allow lower input levels, say 0.707V doesn't mean it can accept any source input level above 1V. Impedance, distortion, noise and all that are still in play. As with anything in life, changing that has consequences, failure to address that can lead to problems. Gain structuring is something most people, even the technical ones do not understand nor have an idea of what it is. Designers and manufacturers adhere to these so that their products can be paired, to a sincere level, with any known sources out in the market.
For commercial/home use, it is normal to see input/output levels between 0.5V up to 5V peak-to-peak, for pro use, 5V is a standard level without signal clipping.
Parang hindi na practical.
That's why there are numbers and conventions.