In the grand scheme of things, that's not necessarily true even if you are potentially correct in saying this.
There's enough evidence to suggest that Ella is also a half and half, or at least close.
1. Ella says that she and MC are the same.
2. Ella has dealings with Memory who wants a half and half.
3. Ella is deemed a failure by Memory, not Body.
4. Ella says that she was "never good with Memory", which points to having some, probably minuscule, part of the trait.
Ella has obviously a better version of the Body trait than MC, but if we go by compatibility percentages, she shouldn't be that much more compatible, not to the point of being a prodigy like she is presented to be.
There's also the idea that Apostle spawns are fundamentally different which may affect how this thing works. There's a good chance that MC with only a single trait would be significantly better at it, despite his 50-50 genetic makeup.
In any case, after lurking a bit on the streams and asking WW about stuff like that, it seems like a lot of things are either intentionally misleading or just plain wrong. Syla's words should not be taken seriously without confirmation from another source.