Damn...tough one.
Walker was powerful enough to actually threaten Death though she did destroy him. He also treated Thor, Thanos, and Genis-Vell like children.
JSA Mordru fought Nabu across multiple universes, their power was sufficient to travel between alternate timelines with ease. He also beat Thunderbolt and after being thrown into the Rock of Eternity and thus weakened he still had sufficient power to take a full blast from ROE-Shazam, a blast that left Shazam with barely enough power to stand. He then casually restored Shazam's power so he could fight the Spectre who Mordru wisely wanted to be occupied.
Mordru takes a very slight majority or its a split.
__________________
“Where the longleaf pines are whispering
to him who loved them so.
Where the faint murmurs now dwindling
echo o’er tide and shore."
-A Grave Epitaph in Santa Rosa County, Florida; I wish I could remember the man's name.
The fight was very impressive on Shazam's part vs. the Spectre considering his state at the time. If it wasn't for the whole I can absorb magic thing Shazam would have probably won.
I dunno, surely Shazam might have been able to hold him in check long enough for the other mages to get rid of Eclipso and set things straight but as it was shown later you can't really destroy the Spectre force so Shazam really couldn't have 'won'.
You are picking and choosing which statements to accept. The Spirit admitted he was almost destroyed by Marvel who batted him around like he was nothing. To scare the Spectre and for someone to have to aid him in escaping makes me believe it to be an accurate statement.
Its quite possible that the Spectre himself wasn't aware that he couldn't be destroyed. He's never been rendered powerless before then and its been more or less confirmed that only the host can "die" and the Spectre force usually returns to Heaven to receive another host.
Marvel never "batted him around like he was nothing" they had a long, drawn out fight that was pretty even for the most part and keep in mind that he was never truly in possession of all the power he had "absorbed" as Alex Luthor was siphoning power away.
But still its not like Amped Marvel was some Herald level character, he had in his possession pretty much all the magic in the universe that the Spectre (and Alex Luthor's tower) hadn't absorbed.
I wouldn't say he was being crushed. Cap had the upper hand but Cap would have lost in the end even if Enchantress hadn't lost it. His body couldn't hold that much power.