The default terminal for KDE is
KDE is Qt5 based using KDE Framworks 5, so Qt5 & KF5 libraries & toolkits will already be in memory (RAM). It's use will be fastest, and not waste resources (esp. RAM)
Konsole is Qt based (the upper-case K is commonly a clue as to being a KDE/Qt based tool), thus will use libraries already in memory as they're being used by the KDE desktop itself.
gnome-terminal is GTK3 based, so it's use will cause GTK3 or GNOME libraries to also be in memory, thus will involve a resource hit, which maybe minor if you've plenty of RAM and can afford the hit, but on a RAM limited box every hit (wasted KB or MB of RAM) counts. This resource hit will worry you less if you're going to be using other GTK3 programs that will also share those libraries, but it's still a hit.
As the default GNOME desktop is GTK3, using
gnome-terminal has no costs there. The reverse would apply, ie. the use of
konsole on a GNOME desktop would waste resources and be inefficient.
Other alternatives exist, eg.
qterminal is Qt5 based so will use less resources than a terminal that uses almost nothing already in RAM. There are many choices, but don't forget efficiency, unless your box has fast processors & heaps of RAM thus don't need to worry.
My point is there are reasons for the decisions made, and your choice will waste RAM. (why each flavor uses it's own unique terminal which is most efficient in the chosen desktop).