Re: Why these techniques?
I read sometime ago, a new student asked a aikido teacher are there any specific technique in the aikido armamentarium to deal with boxing, muay thai, wrestling etc.
He answered, "I don't know, samurai did not box nor wrestle."
This brings to attention this: Samurai are warriors and their job is to wage war for their overlords. As a professional soldier, what is the best way to dispatch an opponent? Weapons of course. Bow and arrow for ranged attack, naginata, katana for close quarter combat, tanto and jujutsu as a back up weapon if something should go wrong.
Wrestling/newaza? Unlikely their main strategy; at most basic and rudimentary knowledge, just enough for them to get up, regain weapon and re-convince battle.
Also, boxing or muay thai type kicks are mute for them. These guys are heavily armoured... it is not going to be effective on them. OTOH, kansetsu-waza to prevent deployment of above mentioned weapon; nage-waza to fell an enemy followed by weapon deployment are IMO more useful strategy.
With these in mind, I think I do agree with Chris Hein and similar thinking posters that aikido, or rather its parent art Daito-ryu, are weapon derived art.