Shadorne a fuse is an internal part along with caps, diodes, resistors, wire, trannys etc.... all these internal parts do impact the sound assuming the unit is designed properly as you say. A properly designed tube amp does benifit sonically when higher quality parts are used like Duelund caps, Vishay nude resistors, film caps in the power supply, silver wire trannys, and a better quality fuse. It’s all in the soup.
This also holds true for any piece of gear. Parts matter beyond just hitting spec.
So in the end any well and properly designed piece of gear can sound good and even very good without upgraded caps, resistors, trannys, and fuses. No need for these boutique parts in well designed gear unless one wants that next level of improved fidelity. Power cords do the same thing as boutique parts often times. You are most happy without the boutique parts and that is most understandable. Nevertheless, these parts including fuses, wire, and cords do often improve fidelity. If not, then buy one of the many pro sound amps which are properly designed for $300 and that would be as good as it gets and this whole site/hobby is really useless. I know it is useless for many perhaps including yourself which again is perfectly reasonable and understandable. However, others have the need and appreciate what is possible which is also understandable.
This also holds true for any piece of gear. Parts matter beyond just hitting spec.
So in the end any well and properly designed piece of gear can sound good and even very good without upgraded caps, resistors, trannys, and fuses. No need for these boutique parts in well designed gear unless one wants that next level of improved fidelity. Power cords do the same thing as boutique parts often times. You are most happy without the boutique parts and that is most understandable. Nevertheless, these parts including fuses, wire, and cords do often improve fidelity. If not, then buy one of the many pro sound amps which are properly designed for $300 and that would be as good as it gets and this whole site/hobby is really useless. I know it is useless for many perhaps including yourself which again is perfectly reasonable and understandable. However, others have the need and appreciate what is possible which is also understandable.