@Joker,
My understanding was that this is an open ended discussion thread to propose any theories and possible explanations for what happened in this episode, not a debate. It's okay for me not to utilize every possible point in favor of lowballing Ahsoka just to get my d1ck hard over the internet.
Sheev laughing has nothing to do with whether he's toying or not, holding back or not, whatever you want to call it. He clearly likes to make audible noises that reflect his position of power in battle; whether that be laughing when he believes he's winning or yelling/groaning when strained.
Here is what is known:
• Right after casting the initial spell Sidious was audibly groaning/grunting when pushing the flames through the portal and towards the jedi duo, even before Ahsoka started defending herself:
https://youtu.be/Yg8mUrtHjRQ?t=1m10s
• Once the jedi ran away Sidious again was audibly strained just trying to keep the flames moving at the running pace of the two jedi:
https://youtu.be/Yg8mUrtHjRQ?t=2m13s
• His facial expression here coupled with his cry of defeat when Ezra escapes insinuates that Sidious was putting forth 100% of his effort at this moment:
https://youtu.be/Yg8mUrtHjRQ?t=3m19s
• This pyrokinesis-type ability that Sidious was using has never been seen in canon before, so we have nothing to compare it to. I know I said to not use legends when discussing canon feats, but I believe in this case an exception can be made.
Unlike force-lightning, the power of pyrokinesis does not stem from the direct energy of the force-user themselves. Instead it is generated through the energy of rubbing air molecules together. In the Plagueis novel, Palpatine uses pyrokinesis to kill Pax Teem. It's explained that the effort needed to wield the power increases as the flame grows due to the user needing to both direct the holistic inferno as well as focus on the atomic-level kinetics to create fire.
This idea is reflected in the Rebels episode. Palpatine appears to need his full concentration and power towards the end of the encounter as the flame grows larger and larger while chasing Ahsoka and Kanan. It's reasonable to assume that less effort was needed for the initial attack due to the smaller flame size, but it's still a demanding task when you compare it with the concentration Sidious needed in the Plagueis novel just to flame-up a room.
So,
• Ahsoka was likely only defending against an indirect form of Sidious's power, as the power of pyrokinesis stems from the energy of molecular kinetics and not the user.
• Whatever residual amount of direct-power Sidious was implementing into the attack was likely a reduced version of what Tano would've experienced had Sheev been in person because a significant amount of that power had to be dedicated to controlling the actual inferno size, which was quite large as it covered the distance between Sidious, the portal, and jedi duo.
The above point about pyrokinesis negates anything else you said, as we're now talking about an indirect form of Sidious's power, but in case you only want to stick to canon only (in other words ignore the Legends explanation):
You said:
"t really doesn't. Palpatine would indisputably use all of the power at his disposal given the stakes and importance of his goal. Palpatine wanting to capture Ahsoka and Ezra does not preclude him attacking them at full-power enough for them to be rendered either incapacitated or fatigued enough to fend off his attack any longer—and seeing as how we're talking about Palpatine, that's still a lot of power."
Yes Palpatine has all his power at his disposal, but this doesn't mean he's not prone being blinded by his over-confidence as he's often seen to be:
a. instead of immediately defeating the Maul brothers as he was capable of doing so, he played around with them believing that he could end the fight at anytime he wished. This came close to backfiring for him when Maul briefly gained an upper-hand towards the end of their fight.
b. instead of gutting Mace Windu when given the chance (remember when he holds the saber to his chest?) he again plays with his opponent. Like with Maul, this backfired again and his opponent was able to defeat him.
c. Sidious underestimates Yoda after over-whelming him with thrown senate-pods. His over-confidence and enjoyment of the situation causes him to fail in seeing Yoda's lengthy counter attack.
I would suspect that his over-confidence again prevented him from obtaining his goal in this scenario. He stopped attacking Ahsoka not because she was briefly stalemating him, but because he wanted to enjoy seeing her fatigued and helpless against him. We know this because Sidious was laughing right after he cut off his attack. He wasn't concerned or strained like he was when Yoda was absorbing his lightning in RotS.
Given how much pleasure he was taking in the situation, we can deduce that Sidious was at the very least not putting in the same level of mental effort that Ahsoka was—which was a fight or flight response.
I have don't have any tangible evidence to justify my theory of Palpatine's altar power being weaker than his personal power as it's only my interpretation. By definition all interpretations are valid, but some are more reasonable than others. Why is it reasonable? Well:
- Palpatine was manipulating the flames of the altar to reach out to the jedi. They were not stemming directly from his person. If they were, would it make any sense for Sidious to be straining as hard he was towards the end to keep the flames moving at a running pace? This would suggest that Palpatine was only manipulating the power of the altar, in the form of flames, to reach out to the jedi. He wasn't attacking personally.
- We saw that Palpatine was only able to reach into the omni-dimensional portal once his magic flames made contact with Ezra. This means he wouldn't have been able make any contact with the jedi until this happened. If Sidious was utilizing his personal, physical powers they wouldn't have been able to get through the portal because he couldn't get through the portal himself.
Unlike anything Mother Talzin has done, Sidious was attempting to enter into another dimension altogether. His personal power transferring into that realm would've been next to non-existent.
Ahsoka diverted the wave of flames; she didn't absorb it. The fire wraps around them because they're altering its flow. The initial attack from Sidious wasn't concentrated, it just looks like that due to viewer angle. Plus a few seconds later you can see that the wave of flames ahead of Tano are are just as large as the one behind her.