here's a few things to highlight about this design.
First of all, the scripted nature of its actions went over very well in play. Creating a sense of progression each round allowed the players to make meaningful choices in the face of an enemy. They knew that clumping up was a bad idea. The teleportation effort encouraged them to spread out, but it also meant that they risked being picked off.
The combo of the area push effect with bone spikes' slow allowed the dragon to herd the PCs together to hammer them with its breath weapon.
I use a death saves variant, posted on this Patreon a few months back, where characters at 0 HP stay conscious while they roll death saves. That rule makes D&D deadlier in my experience by keeping PCs who are on the verge of death available as targets for attacks, potentially killing them. On the other hand, that rule also allowed the party to eventually defeat the dragon. A few characters were one roll away from death, but staying on their feet and contributing let the group carry the day.
The dragon's design might seem counterintuitive. Traditionally, D&D post-3e relies on overwhelming variety to try and solve the issue of solo monsters. The idea is that by putting lots of options on a monster, the DM has something to turn to that can counter a group.
I'm not sure that path is viable. In competitive game, a deck or character that tries to do everything always has a weakness that a specialist can exploit. A monster faces four or more specialists! That insight prompted me to consider specializing solos, giving them a relentless script that grinds down the party.
I am not going to say that this is the answer to everything, but I think it's a potentially interesting path. The nice thing is that this approach is far more testable. A simpler plan is easier to adjust in the face of a flaw. Moreover, a simpler plan is also much easier for a DM to execute, as opposed to asking a DM to navigate a full-page stat block.
In any case, this approach has held up across several encounters and monsters, so I am excited to explore it some more