Why is the Profundity Bonus Tier so Painful?

Your reply got me wondering how much "work" are we talking about. If we start out with 80 shards and need 330 to 7*, that's 250 or 25 successful runs total needed after unlock. At 3 or 4 minutes per run x25, how much time is that? It will also take multiple runs especially at lower stars so let's say it takes an average of ten minutes per 10 profundity shards. That's over four hours total play time to unlock at 7* without buying shards outright. I like the idea of Nuking it myself ;) Keeping it under 2 hours!! yikes, could it really take that long?