While I am no antenna expert, my experience with Radio Frequency (RF) from CB to millimeter wave, is that the antenna being used is hugely important. And bigger antennas are almost always better.
From what I have read, the HE is considered to have a weak and not great antenna. When you take apart your HE C7 hub, you will find a bit of foil on the bottom of the case that acts as the antenna. One for Z-Wave and one for Zigbee.
I have voided my warranty and added an external antenna to my HE (7). By adding a very cheap 5db gain antenna, I instantly increased the number of devices connected directly to my hub, by 30%. This also reduced the number of hops for other devices that are still being repeated.
I suggest that on Hubitats next model hub, they provide for the addition of external antennas. I appreciate that not everyone will want to incur the cost of external antennas, or the looks. I also appreciate that this will result in a very slight increase in the manufacturing costs of a hub to add u.fl and/or SMA connectors to the circuit board and case. Though, I believe the additional cost would be far less than a single Z-Wave device. Finally, I believe that the majority of Hubitat Users would welcome and pay for the better RF performance provided by an external antenna.