I've taken a look at 4/3/74 and 4/11/65 under the lens of more modern, EF-scale rating standards, and it's almost amazing how similar they and 4/27/11 all are in terms of intensity. Just based on my non-expert analysis, 4/27/11 actually has the most violent tornadoes overall, but it's very close.
For what it's worth, based on what I could find here are the violent tornadoes in these outbreaks based on Enhanced Fujita scale standards.
Palm Sunday 1965
Midway, IN - EF5
Sunnyside, IN - EF5*
Toledo, OH - EF5
Pittsfield/Strongsville, OH - EF5
Tipton, IA - EF4
Crystal Lake, IL - EF4
Rainbow Lake, IN - EF4
Manitou Beach, MI (1) - EF4**
Kokomo, IN - EF4
Manitou Beach, MI (2) - EF4
Lebanon, IN - EF4
Lima, OH - EF4
Sidney, OH - EF4
Total: 13
*The Sunnyside tornado was borderline, but the intense debris granulation probably would earn it a marginal EF5 rating.
**The first Manitou Beach tornado was probably just below the EF5 threshold, similar to Tuscaloosa.
1974 Super Outbreak
Xenia, OH - EF5
Brandenburg, KY - EF5
Tanner, AL (1) - EF5
Guin, AL - EF5
Daisy Hill, IN - EF4
New Point, IN - EF4
Parker City, IN - EF4
Sayler Park, OH - EF4*
Monticello, IN - EF4
Mannsville, KY - EF4
Frankfort, KY - EF4
Jasper/Cullman, AL - EF4
Tanner, AL (2) - EF4
Broadview, TN - EF4
Total: 14
*The Sayler Park tornado was another which would probably have been rated high-end EF4, but probably not EF5.
Considering how similar the three outbreaks are, it's possible that this is about the upper limit for a tornado outbreak in this climate. It's also possible that there really are freak, once in 500 year events, like the 1974 outbreak was thought to be for a long time, that actually would produce insane numbers of violent tornadoes even under EF scale standards. If so, let's hope there isn't one in any of our lifetimes.