well that's the point i guess in the long term solo mining is more profitable as long as hash power is decent enough for the current difficulty of coin he's mining.
In my experience with solo mining, you don't just need a "decent enough hash power", you need a lot of it, so that you find multiple blocks a day. Basically you gotta be a small pool on your own (and running an actual private pool just for yourself is often the way to go). It will, of course, depend on the coin: with more "stable" coins, the ones where difficulties don't jump up and down all the time, it's possible to solo mine with just a block or two a day and still get reasonable amounts of coins — any bad luck will eventually get "evened out" by some good luck and your earnings over a longer period of time will be adequate. But with the less stable coins you do need to have enough hashing power to find many blocks a day, or you'll just miss a lot by simply not finding anything when some nicehash dude (or a multipool) connects and brings the network diff up 2-3 times for a few hours. If you were mining on the pool at that time you would still be getting something, but when you solo mine there's a good chance that you won't find any blocks during those periods. And so your total earnings from solo mining over the longer periods of time will be noticeably lower than if you were mining on a pool. There's a lot of coins like this, where random nicehash fellas show up from time to time, harvest whatever they want and then get out. I've seen this many times, the network hashrate (and the diff) increasing up to 10x the normal diff for 4-8 hours, and then gradually dropping back to usual.
So solo mining as a means to make more money only works if you have tons and tons of hashing power. At least that's my experience with a few coins I tried over the years. Folks with only a dozen or two GPUs are likely to earn the same or more when mining on pools.
