From my experience it seems the average TV tuner is more sensitive than the Tablo tuner (s), although I cannot quantify the difference directly.
If you have a TV that shows reception signal strength, you might want to build a table of your TV reception readings for each channel for reference. You should only need to record the “.1” channels and skip the sub channels.
If the problem channel on the Tablo also shows a lower reading on your TV signal meter or bar chart, that could be a clue the Tablo might be at the “digital cliff” based upon its tuner characteristics, whereas your TV tuner could be more forgiving. If the weak channel dropped slightly in signal strength or SNR (signal-to-noise ratio) your TV tuner might wigg-out as well.
At my house the weakest TV signal reads 63 out of 100 on one TV and 26 out of 100 on a different brand TV, but both show a clear picture. It is really hard to maintain consistent picture quality if the antenna receives some very strong signals and some weak signals as well. Even an amplifier might not help the weak signals for risk of overload by the strong ones.
There are online services that could help you understand your potential reception issues, like tvfool.com to name one.
Check your reception at different times of day and different weather conditions, as both affect TV signal strength and SNR.
Enjoy your new Tablo and try to accent the positive and play down the negative.