Firstly, the hybrid nature of a plant does not disqualify it from being called a Bean leaf. In fact there is a Darwinara rainbow stars that was made using a Tamakongo that squarely and indisputably lands in the category of Mameba. Because this plant is a dwarf compared to other plants of the exact same hybrid cross, it is still a mameba.
Source: Negieorchids.com
In any case, in the end it is all rather subjective where the boundary between mameba and standard leaf is. Way back when there weren't as many varieties before seed propagation was possible, it was a lot clearer which ones are mameba and which ones are not. There were only a few hundred varieties at most, and since all named varieties at that point were strictly divisions of each other, there were far fewer subtle distinctions between plants and varieties. Back then, it really was clear whether it was mameba or not mameba.
But since the 80s when seed propagation gave rise to an exponential rise in the number of named varieties, and also gave rise to seed propagation of individual named varieties, the boundaries blurred. When you seed propagate a plant, you often introduce subtle variations to the genes that would never happen when propagating strictly by divison, and you end up with single named varieties with specimens that vary greatly in their leaf lengths, among other traits.
While there are some varieties, like Tamakongo, that when selfed will always create mameba offspring, varieties like Raikomaru, will not do the same. Regardless of the controversy of the genetic purity of the variety, Raikomaru is a modern variety that was only discovered in the 80s or 90s. The variety was found through seed propagation to begin with, and it continued to be propagated by seed. Unlike Tamakongo, Raikomaru when propagated by seed will create a wide range of leaf lengths from long to short. Because of this, there are many strains of Raikomaru that have various leaf lengths. There are some that are indisputably bean leaf varieties, and many that are long leaf. There are just as many in addition that straddle the division between the two, blurring the lines.
What can be said though is that some Raikomaru are mameba (although those are usually selected out and renamed) but the majority are not. You really have to look at the individual plant’s characteristics and compare it with public consensus to decide if it is mameba or not.
This is much the same with many other modern varieties. After the boom in the number of named varieties, the lines between mameba and standard leaf have blurred considerably. This has resulted in a wide range of seemingly arbitrary or irrational labels of certain varieties. For example, some people will call the variety Yokozuna a mameba variety. Others insist that it’s not. Because there are no strict objective definitions that define the characteristic there will probably never be a consensus for some varieties.