I believe that the FCC will allow the same power level for either 1.0 or 3.0.
ATSC 3.0 has modulation characteristics that can be chosen by the licensee. For instance, 25 mb/s will have the same signal to noise ability as 1.0.
it is more likely that station will choose a variety of modulation schemes for multiple services. A useful combination would be mobile video with a low s/n ratio providing audio and low resolution video that can be tied to higher resolutions. This would mean that the audio could continue even if the video were to freeze or stutter.
ATSC 3.0 has two significant advantages over traditional OFDM as used in European DVB-T transmissions. In fact, DVB-T2 was developed by the IBU to take advantages of new technology to improve the noise performance of DVB-T. ATSC 3.0 is based on the modulation advantages of DVB-T2, but using IP encapsulation.
Impluse noise in ATSC 3.0 is significantly reduced by time interleaving of the data. ATSC 3.0 also uses low density parody checks (LDPC) to improve the s/n performance for both white noise and impulse noise.
In my opinion, ATSC 1.0 performs poorly with impulse noise, so 3.0 should be a vast improvement.
As with any rf signals, narrow bandwidth signals out distance wide band ones using the same power all things being equal.
However, the ATSC 3.0 OFDM format should compensate for this slight disadvantage.