There is no difference between fast small rock and slow large rock. The momentum is the same. You don't know if they are loyal or fast. That's the problem. There is no way to tell. Also we're not trying to penalize people for choosing different coins. It's the sudden switch, that's the problem. It's like soldiers don't march over a bridge (a pool). The synchronized force can cause the bridge to collapse. The solution is to randomize the force, not penalize it. Buffer it, add some cotton, soften it. Stop treating the miners like two year olds. Some of them don't care about coins, and they have a right not to care. Maybe they have bills to pay. This isn't a college fraternity. It's a community. People come and go for various reasons.
Now, the difficulty level goes way down, and it is easy to mine blocks. The low hashrate loyal miner continues mining through the pool, and he pretty quickly earns 0.054 coins and in the process extinguishes the 0.054 loyalty credits. A non-loyal slow miner who did not earn loyalty credits contributes the same amount of hash to the same pool (jumping in for the easy difficulty), but not having earned loyalty credits during the previous high difficulty era, receives only .027 coins, per rules of the coin.
There is MORE than one coin. The fast hoppers don't leave at high difficulty in one coin. They leave when other coins have lower difficulty. You could have high difficulty and fast hoppers staying because another coin has higher difficulty or lower reward. Then the hoppers would get the reward while the slow loyals of the other coins get half rewards because they couldn't afford the electricity to mine during high difficulty.
What you describe really is no problem, because you can start mining any time you want you will get adequate compensation in coins. There is no "penalty" in the sense of your wallet losing coins. It it just that when you jump in when things are particularly easy, and you have not mined recently when things are hard, your per-minute-of-mining profitability is more boring (cut in half but still profitable). Rest of the time, when difficulty changes are not extreme, you can jump in and out without any effect on block reward values. But it would train people to moderate hyperactive jumping-in behavior during the rare short-term incentives of apparent high profitability. The system/protocol is set up specifically so trying to jump in and cherry pick easy profits fails. The easy profits are reserved for people who provably were around mining during the recent tougher times. They deserve that reward. Otherwise, everything works exactly the same, you believe in the coin, you jump in without checking anything, stay through multiple difficulty swings, and generally, you are credited the full amount. It's just in the rare case you jump in conveniently when the difficulty happened to be very easy, then it's going to seem (just for that one brief difficulty period) like the reward rate is not exciting (closer to typical profit than extraordinarily profitable). Once you "serve out" one difficulty cycle, you are on exact equal grounds as everyone else. This is
completely fair and totally temporary. The loyalty credit system does not have a long memory as to who has been loyal (except for the few coins you may have earned more of that you still have sitting in your wallet). There is no systemic problem, and hashrates are systematically modestly adjusting all the time, without the crazy spikes caused by short-term profitability seekers. The incentives are for once matched up with what is valuable for the coin network - its security and stability is better served from longer-term hash contributions that come regardless of difficulty changes - than by the same number of hashes that only show up during easy difficulty times. I doubt anyone does this, but think about it - if someone were to hash Catcoins only during times when difficulty level is high, and stopped mining when it got easy, they are helping the network far more than someone who does the opposite - yet they are compensated far less.
