Is there any print quality difference switching from brass to steel nozzle? Brass has better thermal conductivity compared to steel or hardened steel but it has also far less wearing resistance especially compared to hardened steel that among brass and normal steel has the worse thermal conductivity. Basically all 3D printer use brass despite is softer and also more expensive metal than steel. Shouldn't the lower thermal conductivity impact only the time needed to bring it to the established temperature? Is there any noticeable difference in print?

The thermal conductivity will certainly affect the time necessary to bring it to temperature, but will also require adjustment to flow rate with respect to speed of travel. The increased time for heat to travel to the nozzle is reflected in the increased time for heat to be "restored" as the filament transfers it from the nozzle to the bed and to the air.

If you make no other adjustments than waiting a bit longer to heat, you may see print quality changes. You might not, if, for example, the current temperature is a bit higher than needed. Unchanged, the effective temperature change required is compensated by the wider range of temperature allowed by the filament.