The last two are 'magic' and electricity is a technology medieval setting probably shouldn't have, even as 'rare' technology (electric bulb was developed in the late 19th century.) As for the others, how do you design a whole class around them? They are just skills or tool proficiencies.
Well to me Truenaming and Mad Science aren't magic. They are their own forms of knowledge that follow their own rules to create effects.
You could have them be magic in some world or you can say that the presences of magic has warped biology, chemistry, and physics enough to create effects that are impossible on Earth.
As for electricity, so what if we harnassed it recently. There is nothing against a few geniuses brave enough and lucky enough to discover electricity in their medieval era. If fact, based on how electricity was first seen, it would make sense that only a few people could harness and use it as most people would see it as as or even more dangerous than arcane magic.
As for Surgery, Drugmaking Batttlefield tactics, Law, Speechwriting and the like, they would not been their own class. The loremaster would learn applications of them in small bitesized chooseable class features much like invocations. Perhaps at the cost of some "brainy resource".
again, skills in 5e barely define what can be done and what the DC is. It's all up to the DM and the player's opinion and creativity. The loremaster or scholar would allow the group to lock down the effects of some mundane lore of the world to some knowable effect and explain the fantasy of the world should they choose to allow it.
Do the Duskblade and Swordmage have to be their own classes? I could just make a subclass for the Gish for each of them, one getting more spellcasting, and the other getting more fighting power.
Perhaps they can be the same class.
Perhaps you could make a base class gish that gets
•Martial and Simple weapon proficiency
•Light armor profiency
•Fighting style at level 2
•Halfcasting and up to 5th level arcane spells like the paladin and ranger
•Extra attack at level 5
•Some sort of basic Mage-Warrior class feature.
Then you choose a subclass at level 3.
Duskblades get more warrior stuff with heavy armor and shields and maybe a 3rd situational attack.
Swordmages get more magic stuff the aegis of assault teleports
Then you get Staffmaster that goes on a tangent and focuses on skills and fighting with a magic staff.