Two points concerning Aikido's uniqueness of technique (not touching any of the philosophical or spiritual differences)…
I find it a bit odd that people are instantly able to compare "everything to everything" so easily. While our human bodies haven't changed physiologically since the birth of mankind, combative arts based on those bodies have changed a thousand times over and the arts of today are NOT the arts of yesterday.
Those types of comparisons are about as valuable as comparing the abacus to the modern day computer. While it may be amusing (for about one second) to ponder how early on humans developed a device to aid computing -- those "devices" are day and night apart in terms of refinement and applicable usefulness today. I will never use an abacus.
Because Aikido's roots are unique (i.e. how it was developed), its approach to defense is also unique.
The root art Aiki-Bujutsu (or Daito-Ryu, or whatever name they chose to change it to as it was passed from family member to family member) was born out of a time when every samurai carried a sword at all times.
ALL of the movements in Aiki-Bujutsu are based on the sword in some way:
- You are being attacked by someone with a sword
- Someone is trying to take your sword (or control it usually before you have it drawn)
- Many people are attacking with swords (or weapons)
- You are in a Japanese-style building with a low roof and must use Shikko (either to defend against a sword or to use you own sword).
Out of those roots, you end up with a style that is IMO the most comprehensive martial art on the planet.
Aikido will teach you to:
-Defend against almost any weapon (since most weapons are used by the hand)
-Defend against being grappled in almost any way (not all ways are taught by every dojo, but there is usually a way none the less)
-Defend against multiple attackers (in the same way you defend against single attackers)
-Defend standing up, or in Shikko in low ceiling scenarios (not everyday certainly, but when it happens you are in the advantage to the guy that's hunched over)
Furthermore O-sensei refined those movements (very evident from watching Daito-Ryu of old - very stiff and rigid), and those smoother movements better enable handling multiple attackers (IMO).
Best of all, because of it's diversity it is still VERY applicable today. Very few arts can boast being able to handle so many diverse types of attacks, with a consistent mechanism.
So while yes you may have seen one or two Aiki-like moves in other arts, how many of those arts even address that list above? Not too many I'll wager