Shazam prep at RoE was probably superior to what DoV Marvel threw at Spectre. Mordru tooled him at the RoE and then restored him for lulz iirc. I know abc logic generally not good logic but it gives an idea of Prime's magic resistance at that scale. That being the case if Prime's magic resistance based off that showing is in fact that good it might not even be necessary for him to have GA amp to win. Mind you this would be nothing against Captain Marvel, just a case of a supremely bad matchup depending on how much faith you want to put into the Mordru feat, which I hold in high esteem because I'm a Mordru fan and to see him get no sold the way he was, was either supremely disappointing at how far he had fallen or a supremely amazing showing for Prime for the ease he punked Mordru.
Again in the super heavyweight tier Prime tends to do extremely well.
a Group of Guardians,
The entire Green Lantern Corp. wall
DOV Billy beating on Spectre (even as Enchantress was severing the power feed) was far more impressive than GA Prime slowly losing to Monarch. In this instance, true. When Hallax was empowered by Ganthet's energy precipitating Zero Hour, arguably not so much.
Hallax was powered up by several things. However prime easily shrugging off Kinetix's blast (she absorbed all magic in earth 247) and mordru who absorbed all magic in 30th century makes this harder to judge.
To add, Prime would have his amp longer in this fight than the period of time he was fighting Monarch. The amp was already being drained by him doing interdimensional traveling at the rate he was.
I say both amps wear off at about the same time but Prime is able to hang in there due to his magic resistance. It's just hard for me to see magically amped punches doing Prime in. Especially with a GA amp.
^ Trying to account for GA Prime's energy loss while traveling interdimensionally while not accounting for Enchantress completely cutting off Captain Marvel from his amp reeks of a rather puerile double standard.
Beating the sh1t out of Spectre is more impressive than... not really beating the sh1t out of Monarch. At all. I don't know how much simpler it can get. DOV Captain Marvel's punches aren't Black Adam's punches.