Sure, both pokémon will take more damage, but while the raid bosses have a fixed HP (although it could be updated), the attackers will have more HP, which can make them bulkier (you're not attacking with Blissey right? :) )
Si yes they will be easier IF raid boss HP is unchanged. And if it is, while attackers still have the same power, the clock might be a bigger problem than before.
Magmortar is not good, but it could be an interesting gym sweeper, especially in clear weather.