Spoiler: show
yeah the gods were weakening without pray of humans. Ares on the other hand was getting weaker but during battle most soldiers pray to him to help them fight so he was getting some strength while other gods were less than lucky. Most people just kind of stopped praying due to various feats demigod beating kraken and taking down Hades and other demigods and humans were having adventures and beating titans and various monsters so a lot more faith went into man vs the gods who were a no show for such events. There also some who believe they were better than gods like in part one where Hades show them how human they are one of my favorite scenes from series.