While the "trend" is that newer gear usually yield better results, in some measurable form for DxOMarks, exceptions do exist such as the newer Nikon 24-70/2.8 with VR versus the Nikon 24-70/2.8G lens see here.
While I don't work for, nor defend DxoMarks, it should be notes that making the goal of making newer bodies/lens may not always be sharpness in my example. It could be that they wanted to add VR and in doing so, sharpness is reduced for the lens as a whole. VR is a very helpful tool and in adding it, something had to be taken away or compromised.
As other have noted, making lens is a dance of difference compromises, especially faster lens such as the f2.8 zooms or even top end primes. I can only assume that in making the E-PL7, the designers has some goal and either using a sensor that could resolve images better wasn't in the equation or even the coating on the anti-aliasing filter reduces sharpness. Perhaps a firmware update could fix it, I really can't say.
The only thing I can say is if you really want to test it, rent it or borrow it and see for yourself. If the sharpness is noticeable and you do care about it in the images, don't upgrade.