Solid write up!
I do think Pillar is an extremely powerful card and I would not be upset if it was changed but I also do not think it breaks the game or forces you to put it in every deck.
So, for the sake of discussion, I will dig into this a bit more to examine what makes Pillar appear so much better seeming than other options.
Pillar of Righteous Flame is first and foremost an EPIC card. This means you can only have 1 and in this respect if you look at most other cards with the epic trait, you'll see that they are far better than their non-epic counterparts, for good reason because you can only have 1 ever.
With that in mind, let's look at some easy to compare cards 1 epic and 1 not.
Heal - Quickcast - 9 mana - holy 2 - living creature - 8 dice
Lay Hands - Quickcast - 9 mana - holy 3 - Living non-mage creature - 12 dice and infinite condition removal for relevant cost
So the first major difference of course is that Lay Hands cannot target the mage, which is a reasonable downside because that is the most important creature there is and the one you'd likely want to heal most. However, quoting you in from your post:
But highly situational cards are not judged by their worst case, but by their best case.
"
Lets ignore that bit and focus on what it's good at, healing other creatures. Using that we can see that for the same mana it's 1.5X as effective as heal in dice alone and comes with the extra condition removal, if we measure that with another known spell (Cure) that gives you the ability to remove a single condition we can estimate that cost to at least 2 mana because while that spell also heals 2 attack dice, you can only remove a single condition. With this I would estimate an Epic card is roughly twice as powerful as a relevant non-epic card.
Taking this information let's go back to the spell that I agree is closest to Pillar in function, Thunderstorm. Let's see if we can backtrack and find out where Pillar is about twice as powerful based on the above. So if we first try to measure their comparable attacks we can take two extremely similar light and lightning attacks namely, Arc Lightning and Sunfire Burst.
They both have range of 0-1 / ethereal & unavoidable / arguably similar effects and cost 5 mana. However, notably the light attack has the +2 against nonliving (like Pillar) but
interestingly, has 1 less attack die than arc lightning. By this I think we can agree that pillar has 2 extra attack dice when compared to Thunderstorm with arc lightning and sunfire burst as our models for comparing light and lightning attacks.
So, with this knowledge we could say just by the default attacks Pillar has at least ~1.5X the power of Thunderstorm just by the attack power alone because it has 1 extra dice in addition to the situational +2 vs nonliving.
However, as you noted, pillar attacks on entry which if you assume they both get the same number of attacks is either 2X as many attacks to 1.33X. This is determined by assuming worst and best case for casting the spell (only gets 1 attack from dissipates so adding another attack doubles the attacks, to gets all 3 where it only adds an extra attack out of 3. e.g. 1.33X). Taking into consideration that pillar costs 1.5X mana (3 extra) as Thunderstorm, we could potentially just chalk this extra attack part up to that difference.
But, there is still one more aspect to Pillar that Thunderstorm doesn't account for, which is the free attack on any enemy creature that enters the zone. This is similar to caltrops and bed of urchins as you mentioned, but those are permanent (and removable) vs a temporary barrier. Yet again, there is another significant difference that they cannot attack flying creatures which is impossible to measure with known cards since there is no other card with all these qualities. With this, it should easily put it up to the 2X power threshold of an epic spell if we value caltrops (5 mana) and bed of urchins (7 mana) very conservatively.
This is all without mentioning that there is one other significant benefit to Pillar which is that it only attacks enemy creatures. Caltrops, bed of urchins and even THUNDERSTORM will attack any creature in its zone because it does not make the enemy distinction.
So, overall, while Pillar is obviously a very strong card I don't know if I think it's as egregious or offensive enough to ruin the game. In fact, I wish there were more cards that change the dynamic of the battlefield like Pillar because it changes how you think and makes games that much more interesting in my opinion.
Thank you for the post Enti! I always enjoy reading your insights into the game.