Pandemic's difficulty seems to rest on the placement of the first epidemic card in the deck
According to the official instructions (page 3), the player deck is prepared by first splitting it into multiple piles of roughly-equal size (one pile per Epidemic card) and shuffling exactly one Epidemic card into each pile.  These piles are then stacked on top of each other.

So even in an easy 4-Epidemic game, there will guaranteed be one Epidemic card in the top quarter of the deck (which, being a 59-card 57-card 49-card 48-card reasonably-sized deck, would be within the first 15 12 cards or so); this could be on the bottom of the top quarter, yes, but it's impossible for it to be anywhere near the bottom of the deck.  And even if it is on the bottom of the top quarter, it wouldn't affect the concentration of the remaining three at all, since they're shuffled independently into the second, third and fourth quarters of the deck respectively.

So far as concentration is concerned, the absolute worst case scenario is that you'll get two Epidemic cards in a row; one from the very bottom of its quarter, and the second from the very top of the next quarter.

So while yes, exactly where the first Epidemic occurs in the deck could have a significant effect on how the rest of the game plays out, it's not near as problematic as you've presented as long as the deck is prepared properly.