I don't think so. There are multiple examples of people who added techniques and/or principles of other arts bringing aikido to new heights. I'm thinking of people like Nishio (judo, karate, swordmanship), Yamaguchi (KSR), Michio (bojutsu), Tohei (yoga), Sugawara (TSKSR and CIMA) and many others; I don't see their work as going backwards.
I would argue that they didn't bring aikido to new heights with those things. Those things brought them to aikido, and they were allowed to train with O-Sensei because of their dedication as students. Those arts were part of their influences and offered another avenue to elaborate on a dimension of aiki. Aikido is 'bigger' in an essence, because it brought those skills to new heights.
Like John said above, and I said before him, it is devoloving when we become macro-lateral.
Trust in the path that has been carved for you. Bring all you have with you, and continue to spiral the mountain.
From Aikido Journal today
: "What I’m trying to say is this. In the old days, each master (person) would decide on his own, “I’m good at throwing”, or “My kicking is outstanding,” or I have a great short sword technique.” Then based on this subjective judgement he would set up his own style in a formalized tradition (ryuha). In the case of the “modernization” that took place, the sword was taken out of jujutsu, and likewise, swordwork excluded jujutsu. The arts were divided into specific fields based on the type of technique. An old time practitioner of Ninjutsu, the Art of Stealth, thought only of the real life application. He would do anything he had to do in order to win. This was, of course, because they used technique for the purpose of war, and from that point of view you had to be able to cope with a long engagement distance or a short one, you could jump, do anything necessary. But if we move up to the present we don’t think about such realistic applications. Through our training we forge our spirits (kokoro) and bodies, and so doing we concern ourselves with being useful in more peaceful pursuits. This is the modern way of thinking, and it is so precisely because it is not warlike."
"Though I can’t really say how much he developed from the side of technique, I guess we can say there was a great change based on a “change of heart” (kokoro no tenkan).." -Tomiki Sensei