That simply isn't true, newer iterations don't always, and usually don't, have "higher power" engines, it's an efficiency and cost thing. Why spend money making a super ultra-powerful engine for a sub when it isn't needed? It's a balancing act. It's as strong as it needs to be for what it does. That's even the case in MGS, and why some MGS have smaller or weaker aspects, engines, and capabilities than previous models.
We have no reason to believe that oh is equal to AG, we already know its size and cruise speed is less, given its smaller size, it'd by proxy require a smaller engine too.
And power output, doesn't actually matter.
When you stop say, a speeding car, you don't calc the engine's hypothetical limit and work, ya calculate the work needed to stop its KE.
The actual engine doesn't affect Raiden's feat, what you want to find out is oh's KE in that moment, and the work Raiden did to stop it nigh-instantly. That, would be what he scales to, as that's the energy he exerted to stop its momentum. Trying to find his durability or anything else ain't worth it because ISL would make it like 100000x less than the full yield.
Which is to say, correct the dimensions, and calc Raiden halting it. It will almost certainly still be an upgrade, especially given oh is surprisingly non-hollow.