That is better than selling for potentially $0.00 or paying 15+% (Dai at $1.15+) above the market rate in most cases. So long as the collateral being purchased is diversified I don’t see it as a problem. Everything gets easier as there are more diversified and liquid assets available for the system to use. Right now that isn’t the case yet (which is why this period is hard to navigate).
If Dai was over peg and ETH falling for example: Why add pressure by buying more Dai from the already demand overloaded market? Instead I say MakerDao should sell Dai for other assets and if the price of Dai gets back in line then go ahead and buy it for the ETH.
If not, trade the ETH for other assets as well if exposure to ETH was deemed too high and continue selling Dai until the price is back to Peg before unloading ETH for Dai directly. MakerDao profits by selling Dai into a market over the Peg price and loses in the opposite scenario… Why lose when MakerDao can gain?