This flashback imo is really putting to bed the two major notions that have been passed off as fact for over decades in this community.
1."PK level" being some special tier above top tier as it pertains to individual strength
2.Old gen top tiers being on some higher pedestal compared to current gen top tiers
A Prime WB can still feel threatened by a man like Oden (who I have no reason to believe is on a level above the current gen top tiers), he wasn't immune to this. Top tiers remain closely knit even from that era, Garp, Sengoku doesn't matter who it is, they could give even the PK a hell of a fight. Roger was well into his prime here implied by him running out of time. Sengoku was tossed in this group for the first time really, he is implied as a legit threat to a Prime Roger (backed by Roger's respect for him). This really serves to bring Garp, as well as WB and Roger, back down to Earth with Oda grouping them with the rest (Sengoku representing the likes of Shiki and so on so forth).
Doesn't make sense why the top tiers of the Great Pirate Era (Era after Roger's death) would be weaker in the first place, as the competition would only have grown stronger, giving birth to stronger individuals. Now I'm not saying there are stronger individuals at the very top (Above Roger or WB), but the Old Gen isn't on some untouchable level, any top tier from this era would still be a threat to anyone.
Just like cases in real life, history tends to romanticize the past greats into some untouchable immortal status, that is exactly what occurred here both in verse, and in the OP community. Now that we're seeing these legends first hand, turns out they're human. Not surprised one bit tbh, it was bound to happen imo.
To illustrate what I'm saying: No...Prime Garp is not some demi god who would manhandle the likes of Akainu just because he could give Roger a good battle. That would not be uncharted territory for the Akainu's of this verse to pull off either. I thought Garp was already brought down to Earth when he was shown having a power struggle in a clash against the likes of a 500 mil Bounty Chinjao, but instead the scenes narrative just got controlled to feed the preconceived biases of Old Gen power placement (similar thing happened when Oden clashed with WB, instead of simple credit being given to Oden, excuses were being made as to why WB's strength well into his 40's, wasn't close to his prime).
Roger and WB are simply the strongest individuals above tightly packed competition. That's the vibe I'm getting from the story lately, and that's the direction I feel Oda is going with.