How to improve circuitikz single line diagrams?

Ok, I'll try to answer some of this. Let's start with the list of questions (please, next time, one question per post).

1. Yes, that is true --- I will contact the author to see if we can add a switch/parameter for this (Update: it will be in the next release). For now, I propose a brute-force patch of the symbols.
2. You can make a new symbol request on https://github.com/circuitikz/circuitikz/issues, with references to printed things, and maybe somebody will do it (or you could try a go at it! You'll be welcome!)
3. I propose using a macro, like in https://tex.stackexchange.com/a/597815/38080, but I provide a bus element here if you prefer the to syntax.
4. You were using a non-standard way of setting relative size, try again!
5. I provide two example for positioning a multi-line label, either using the provide l2 facility, or with shortstack and adjusting the distance;
6. I do not know how all those "ground styles" are. Please see point 2.

Now, the code does the following (I have put comments in it; notice that this is a minimal example, so I can work on it and not having tons of repetitions and distracting things...)

1. It starts patching the commands pgf@circ@delta, etc., that are used to draw the transformers' symbols. You can find them in pgfcircbipoles.tex in your distribution. The first three resets the linewidth to the standard one for the circuit, the second three change the size a bit.

2. I define a bus as a very squeezed fullgeneric, with a parameter for the height, and a default of 3 (you can change this; the number are all proportional to the standard length)

3. If you do not want poles, no need to use - in every to command, it's the default.

4. There are two ways to position the label; using l2 is more spacy (and in my opinion readable), using stackengine is more compact --- a matter of tastes, I suppose.

documentclass[border=10pt]{standalone}
usepackage[siunitx, RPvoltages]{circuitikz}
usepackage{etoolbox}

makeatletter
% This should probably be added as a couple of parameters; I'll contact the author
% (see https://github.com/circuitikz/circuitikz/pull/397). But for now, let's just patch
% patching linewidth
patchcmd{pgf@circ@delta}
    {pgf@circ@setlinewidth{bipoles}{pgfstartlinewidth}}
    {pgfsetlinewidth{pgfstartlinewidth}}
    {}{FAIL}
patchcmd{pgf@circ@zig}
    {pgf@circ@setlinewidth{bipoles}{pgfstartlinewidth}}
    {pgfsetlinewidth{pgfstartlinewidth}}
    {}{FAIL}
patchcmd{pgf@circ@wye}
    {pgf@circ@setlinewidth{bipoles}{pgfstartlinewidth}}
    {pgfsetlinewidth{pgfstartlinewidth}}
    {}{FAIL}
% patching scale
patchcmd{pgf@circ@delta}{-.01}{-.02}{}{FAIL}
patchcmd{pgf@circ@wye}{-.015}{-.02}{}{FAIL}
patchcmd{pgf@circ@zig}{-.015}{-.02}{}{FAIL}
makeatother

% define the bus (ab-)using the fullgeneric component
%
tikzset{bus/.style={fullgeneric, %
        bipoles/fullgeneric/width=0.02, bipoles/fullgeneric/height=#1
    },
    bus/.default=3
}
begin{document}
begin{circuitikz}[european] % do not use style={}!
    % this is the correct way to set the class values
    ctikzset{resistors/scale=0.55, inductors/scale=0.55,
         blocks/scale=0.5, grounds/scale=0.55}
    draw (0,0)
    % choose one of the following two
    % to[oosourcetrans, name=t1, prim=delta, sec=wye,  
    %     l=shortstack{$T_1$${}_{24:132}$}, label distance=-6pt] ++(3,0)
    to[oosourcetrans, name=t1, prim=delta, sec=wye,
        l2=$T_1$ and {scriptsize 24:132}, l2 halign=c] ++(3,0)
    to[bus, l=$gs_1$, name=gs1] ++(1,0)
    (gs1.center) ++(0, 0.6) to [L,l=$Z_1$] ++(2,0)
    to [bus=1, l=$ts_1$] ++(1,0);
end{circuitikz}
end{document}

PS You can notice why I prefer the macro for the bus: using the macro, as in the linked post, the bus has a zero width, so that the components between buses are naturally centered. If you use a to[bus... syntax, the component has the size of the path, and you have to take into account the distances by yourself, and you have to manage the leading wires. If you use the definition in https://tex.stackexchange.com/a/597815/38080, the circuit will be:

begin{circuitikz}[european] % do not use style={}!
    % this is the correct way to set the class values
    ctikzset{resistors/scale=0.55, inductors/scale=0.55,
        blocks/scale=0.5, grounds/scale=0.55}
    draw (0,0)
    % choose one of the following two
    % to[oosourcetrans, name=t1, prim=delta, sec=wye,
    %     l=shortstack{$T_1$${}_{24:132}$}, label distance=-6pt] ++(3,0)
    to[oosourcetrans, name=t1, prim=delta, sec=wye,
        l2=$T_1$ and {scriptsize 24:132}, l2 halign=c] ++(3,0)
    bushere{1.5}{$gs_1$}{}
    ++(0, 0.6) to [L,l=$Z_1$] ++(2,0)
    bushere{0.5}{$ts_1$}{};
end{circuitikz}

with this result:

PPS yes, the buses are a bit asymmetric. This is due to a bug in bushere that makes space for the upper label... the solution (any one of them) is left to the student!