Yes you need high C-rate charging
25A would be just OK, but that is **per 100Ah** unit
**if** you expect good longevity from your expensive AGM bank.
Really nothing confusing about it.
If you can't do the one, you don't get the other, simple.
None of this is new, if it surprises you you just haven't been paying attention, dozens of members stating the same, marinehowto.com articles linked to in hundreds of threads.
Now, what percent of optimum cycle lifetime do you lose by e.g. only using solar? Or only getting high amps a few times per month?
Well it's infinitely variable, DoD discharge, how often do you get to 100% Full, ambient temps, all these variable are intertwined, therefore cannot be quantified.
If you are simply unable to care for a lead bank well, then just get a cheap one - but still true deep cycling - so having to replace it more frequently is not wasting so much money.
Many (most) cruisers are in that position.
You spend what you have to, do the best you can, and otherwise what else can you do, just let it go?
Or, you change your plans and usage patterns, for the sake of bank longevity? probably not. . .