I happened to notice an earlier post, but it may not be too low a signal, could be that it is too high & overloading the tuner. TV2 out is sometimes used for more than one set using splitters that drop the signal. The output may be high to compensate for this.
Also, how do we know how well the NTSC tuners are now that manufacturers are using? They may just be "good enough" to qualify as a tuner & the manufacturers are putting the quality components & more attention to the ATSC tuners since the switchover...
Just a thought or 2...