For the past 5-months I have been running a Legacy 4-channel next to a Gen 4 4-channel. Both are connected to separate Mohu Leaf Supreme Pro antennas mounted side by side.
When recording OTA programs the Legacy unit consistently out performs the newer Gen 4 unit in terms of successful recordings.
At least in my case, there is no question that the Legacy unit has a far better tuner than the Gen 4.
I’ve been doing the same thing but with only one Mohu Leaf 50 antenna split between the two. I have found that successful recordings are the same on both devices. I need to use an external inline amplifier going to my legacy Tablo (after the split) but the Gen 4 Tablo works fine with the internal amp turned off, so with no amplification needed. I feel the tuner in the Gen 4 is considerably better than the tuner in the Legacy.