For years I taught aikido, judo and karate. Aikido dojo can differ just as much as karate dojo as far as sport vs practical. Aikido is definitely not "gentle" to uke. The falls and "slams" of aikido are harder, so to speak, than judo break falls. By that I mean they are at bizarre angles and damage to the joints occurs BEFORE the fall begins. For example, the shoulder technique, shiho nage can't even be practiced in the dojo unless it's modified to prevent serious injury. On the street, a shiho nage does massive shoulder damage before the opponent falls. This is why aikido looks so "pretty" in demos. Uke is given smooth manipulations that allow him to do a safe fall out of the technique. In actual use the techniques are snapped. The aiki throws lets the aggressor throw himself and require little to no manipulation by nage. Some overlap does exist with judo and aikido.
So yes, aikido techniques are devastating just as boxing is compared to karate point sparring. Steven Segal's first couple of movies show realistic use of aikido techniques. There is the less destructive side composed of pain compliance, come-a-longs, etc, that are sometimes taught in police academies. Another misconception is that you don't strike in aikido; this is simply not so. O sensei once stated that "atemi is 90% of aikido". Strikes, both feints and actual hits are used in combination with techniques. My sensei, now sadly deceased, taught very small circles as opposed to the grand, sweeping circles that look so beautiful in videos.
