All coins that have multi-pool doesn't have additional coins through PoW. If Pawncoin price rises up due to Pawncoin Multi-pool what stops other multi-pool from mining pawncoin directly due to the profitability. I think the difficulty will be high
But the best option is to reduce the Block rewards to prevent other multi-pool from mining pawncoin and then sell except if they payout in pawncoin.
If mining pawn directly is more profitable then multipool then the diff will rise. If the diff rises the multipool gets more profitable again. Multipool and mining directly will keep each other in balance always making pawn the most profitable coin to mine.
High difficulty only means that the price is rising. Do not in ay circumstance lower the block reward. High difficulty, high price and a lot of miners and people involved is good!