No Direct Hit in HW. Only came out in Stormblood. Increased potencies and Direct Hit make POTD easier than it was, but it's still no picnic when you get deep, regardless. That and, you still can't Direct Hit without Direct Hit food, since substats are set to base inside. Direct Hit functions in the same slot as accuracy, that is to say, at base Direct Hit, you have no Direct Hit %, unlike Crit.
I wish I had more time to do solo runs, would like to get a 200 solo clear out of the way sometime in my life. Plenty of duo and party clears, but solo runs just take so much time.
Well, spinning is different from LoS, because LoS can happen to players too. It's an explicit function of the game's programming. Spinning monsters to prevent their attack from occurring is 100% unintentional, 100% exploit. Monsters in Deep Dungeons are taken from the rest of the game, where positioning monsters and keeping them still is the optimal way to play. The necessary thing for spinning is so out of the ordinary that it's likely they didn't know it was an issue until relatively recently. I assume it's been possible since 2.0's inception, we've just had very little reason to use it.
In regards with using it in a Deep Dungeon Solo run. Well, I've got no objection to others using it. Why throw away 10 hours of your effort if you don't have to? That said, it is still an exploit. It's just not a very major one. I wouldn't expect SE to ban for it. I would expect them to fix the issue. They did fix a somewhat similar issue a few years back where they didn't want casting mobs to be interrupted by tanks running behind them anymore.
Though this does make me wonder, since spinning works on pretty much everything, I wonder if it's possible to use it to cheese raid bosses too lol. If that were to happen, they'd definitely fix whatever thing causes monsters to be unable to attack while spinning.