Yeah, I can understand the frustration. IMHO the Home-Manager way of doing things has some merits:

• You can (generally) manage the installation of packages together with their configuration.
• You can override individual configuration values for different machines (which I guess, you can also do via templating in chezmoi).
• Some programs don't have a particularly readable configuration file or spread this configuration out over multiple files, or save all kinds of additional garbage into their configuration file which you don't want to persist. Home-Manager can work around all these issues, and in such a case is likely also better documented than the original configuration file.

That last point is one that's particularly relevant for me, because KDE Plasma's configuration files are largely terrible. Home-Manager, together with Plasma-Manager, is the only sane way I know of, to automate the panel configuration in KDE.

But yeah, if you don't use software with terrible configuration files, then I can certainly understand preferring dumb templating. I have also decided against using the Home-Manager-specific modules in places, or might only translate into the Home-Manager-specific module when I actually want to vary configuration values between two machines.

Just to give a quick impression of how terrible the KDE panel configuration is, this is a snippet out of the fittingly-called plasma-org.kde.plasma.desktop-appletsrc file:

[ActionPlugins][0]
MiddleButton;NoModifier=org.kde.paste
RightButton;NoModifier=org.kde.contextmenu

[ActionPlugins][1]
RightButton;NoModifier=org.kde.contextmenu

[Containments][1122]
activityId=f588743a-9bab-4f56-8f90-3616085ab6e0
formfactor=0
immutability=1
lastScreen=1
location=0
plugin=org.kde.plasma.folder
wallpaperplugin=org.kde.color

[Containments][1122][Wallpaper][org.kde.color][General]
Color=#79740e

Ah sorry, that doesn't actually show any of the panel configuration, because KDE mixes configuration for the panel and desktop widgets and the Activities feature (like workspaces, but with separate wallpapers and widgets for each Activity) all into the same file.
So, here's a snippet that actually shows the panel configuration, from just a few lines below the first snippet:

[Containments][1807]
activityId=
formfactor=3
immutability=1
lastScreen[$i]=0
location=5
plugin=org.kde.panel
wallpaperplugin=org.kde.image

[Containments][1807][Applets][1808]
immutability=1
plugin=org.kde.plasma.showActivityManager

[Containments][1807][Applets][1810]
immutability=1
plugin=org.kde.plasma.pager

[Containments][1807][Applets][1810][Configuration][General]
showOnlyCurrentScreen=true
showWindowIcons=true
wrapPage=true

[Containments][1807][Applets][1811]
immutability=1
plugin=org.kde.plasma.panelspacer

[Containments][1807][Applets][1812]
activityId=
formfactor=0
immutability=1
lastScreen=-1
location=0
plugin=org.kde.plasma.systemtray
popupHeight=432
popupWidth=432
wallpaperplugin=org.kde.image

What those numbers in e.g. [Containments][1807][Applets][1812] are? Ah, they just count those from 0 to infinity, whenever you add a widget through the UI.
And in case you were wondering since when INI allows for nesting section keys via [multiple][brackets]: It doesn't. That's a custom extension of the INI format, specifically in use by KDE.

Like, man, I love KDE for its features, but this is the stuff of nightmares.

The CSS thing might be true, but the swayconfig file is probably a solvable problem, especially with everything being slowly moving to freeform modules. We just need to write a Nix -> swayconfig generator, which shouldn't be too difficult because swayconfig is not even turing-complete.

Does Home Manager not just have a dot file manager built in? On Guix, I just have my Waybar config. get moved to the appropriate location that Waybar will expect it.

Some services will even allow you to specify files to get injected into the config.; like the Bash service so I can write some definitions out in a .sh file and the service inserts that contents after the boilerplate it provides into my .bashrc.

Well, is it like that using home manager?

I remember home-manager integrated with flakes being a nightmare for my potato laptop because I defined even the bash alias and such stuffs in it and even if I had to change/add a simple alias I had to rebuild the whole system lol, I could have just used home-manager standalone to be honest(I forgot to do this) but I just switched to using the old way of managing dotfiles with stow.

So right now I have it defined in the .config/sway/config file like this:

input * {
    xkb_layout "us"
    xkb_options "caps:ctrl_shifted_capslock"
}

Maybe I will come back to using standalone home-manager one day.

Oof, I was just talking about making things declarative there. If you want to configure it the old-fashioned way, like you would on other distros, then those difficulties don't apply.

In more general terms, though, it's a bit of a double-edged sword. The Nix package repository has more packages than other package managers: https://repology.org/repositories/graphs

So, the chance of finding an obscure software, that's already packaged, is rather high.
Here's the online package search, if you want to check the availability of some of the obscure software you use: https://search.nixos.org/packages

But then, yeah, the flipside is that, from what I understand, you can't just download a random executable off of the internet and run it, because of the Filesystem Hierarchy Standard not being adhered to, as the post also mentions.
You can set up Flatpaks, and I believe AppImages would work, because those also live in their own FUSE filesystem. Well, and there is ways to emulate the FHS layout to get normal applications to run, too.

But yeah, way out of my field of expertise there. I have only one software installed which isn't packaged for Nix, which is a program I wrote myself.
And to get sufficient FHS emulation for that, I just needed this line in my config:

programs.nix-ld.enable = true;

More complex programs will need a bit of extra configuration: https://wiki.nixos.org/wiki/Nix-ld

(I could also add a flake.nix file into my software's repository, though, which would make it so it could be installed straight from my repo, as if it was packaged.)