The fact that it is possible for apps to take on smaller bets themselves (which again, is not happening at the moment) does not affect the investment pool whatsoever.. We tell people that their investment will only take on EV+ bets, and we only allow EV+ bets.
Well, it would definitely affect the Volatility of pool returns if apps are taking all the small bets and the pool only underwrites the largest bets. Of course as you say, that is not happening now. And volatility does affect the pool value in and of itself, so I'd like to suggest that yes, it does affect the investment pool. (A pool +EV with higher volatility is less valuable than the same EV with lower volatility.)
A primary concern of all investors is the prospect of a 'Hufflepuff' type event - you may recall the guy who hacked/broke primedice for an egregious stack of coins. Hufflepuff didn't do that with small bets - he was a 'whale.' So when an app owner takes on the small bets themselves but leaves the largest bets to the investment pool they are in effect hedging their 'hack risk' given the hack will manifest with very large bets.
TL;DR : Apparently an investment in the MP bankroll is not necessarily positioned to underwrite all bets. In fact at any given moment it is not clear which, or what percentage of bets, are being underwritten by the public bankroll, and how much is underwritten by the apps themselves.
Again, I totally believe you that the app owners are not underwriting their own bets with any consistency, and thus it is 'not an issue' ... now. But I think as MP grows, it could be.
Anyway, I'm not trying to be difficult. As an 'investor' I just like to understand what I'm invested in ...