All those ran with investments though, PBMining has not. I'd also guess they've reached their investment peak long time ago ( the point where it'd be the most profitable to run with the investments ).
You could be right but I don't think there is any way to know when they will/have peaked.
Look at the "sent" chart:
https://www.blocktrail.com/BTC/address/1Payday1sm5wGqtatKscfXnxARZ2B2MF3zTheir payouts/customers have been increasing pretty steadily so I think it's possible they have hopes of reaching a higher peak.
Anyways for every reason that they might be legit, there are a dozen reasons they are probably not.
Again, PBmining could dispel all rumors/doubt by simply providing a mining address. Why don't they?