Another potential issue with it is that - regardless of how long it takes to load up - a carrier full of expensive rares at the previous balance could be over 750,000 merits, which is enough to single-handedly fortify a system from minimum Fortified up into Stronghold in the six or so hours it takes to unload it ... and of course you can wait to the end of the cycle to see which (if any) systems your opponents undermined a lot before deciding where to deliver to. I think Frontier have been wanting to get away from "stockpile and hand-in on Wednesday night" snipes with PP2.
Mining is also available as an Undermining action (and with slight modification of where you do the mining, as an Acquisition action)
But that's okay - at any particular time, both sides can use mining equally in a particular system, so there's no advantage gained by either [1]. And it's good that some systems can be fought effectively by mining and some can't, because it encourages people not to get stuck on a single tactic. Sure, it's one of the fastest actions available in the right system. It's unusable-to-almost worthless in the wrong system.
[1] Okay, statistically more miners are on other sides than on your side, but there are other mechanisms in place to balance that out.
