How do ibus-setup, xfce4-keyboard-settings, /usr/share/m17n/, /usr/share/X11/xkb/symbols relate to each other?

In ancient times it was ~/.Xmodmap, then I learned how to tweak keyboard settings via /usr/share/X11/xkb/symbols. Now I have

1. ibus-setup fed from /usr/share/m17n/ it seems
2. xfce4-keyboard-settings configured by /usr/share/X11/xkb/symbols somehow

and both pretend to set up my keyboard. It seems that I get (2.) at startup but as soon as I use the ibus layout switcher (super space in my case), ibus takes over and my layout tweaks in /usr/share/X11/xkb/symbols are ignored.

Can someone explain how these two systems play together --- or not? If I only need an English layout with some hand-crafted tweaks on a few keys, may I uninstall ibus? Or should I rely solely on ibus and tweak an ibus layout?

EDIT to clarify what I am doing: I am using a using my own xkb file in /usr/share/X11/xkb/symbols with the following content

default
xkb_symbols "basic" {
  name[Group1] = "Harald Special";
  include "us"
  key <AE10> { [ 0, parenright, degree, NoSymbol] };
  key <AC01> { [ a, A, adiaeresis, Adiaeresis] };
  include "level3(ralt_switch)"
  include "ctrl(nocaps)"
};

The filename appears in xfce4-keyboard-settings but not in ibus-setup. As described here, I have not tweaked some evdev.xml, maybe this is the problem.

Comment offhand: If you only need XKB layouts, you probably don't need IBus.

OTOH:

as soon as I use the ibus layout switcher (super space in my case), ibus takes over and my layout tweaks in /usr/share/X11/xkb/symbols are ignored

That does not sound plausible to me. ibus-setup makes most of the layouts in /usr/share/X11/xkb/symbols available, and if an XKB layout is correctly tweaked somehow, the tweaks should apply even if you enable the layout via IBus.

To make an additional XKB layout, located in /usr/share/X11/xkb/symbols, available in ibus-setup, you need to add it to this file:

/usr/share/ibus/component/simple.xml

But I still don't understand why you would need to use IBus at all.