Wildfire, and why the proliferation changes from PoE1 went to far.

Ignite proliferation is a tricky thing to balance, I get that. It takes a powerful single-target (well, in PoE1 it was powerful single-target, I'll get to that) mechanic and allows it to effectively clear entire packs with a single action.
This is, sadly, often the ONLY convenient way for an ignite build to achieve clear speeds comparable to even the median viable endgame builds. Ignite the front of a pack, and it spreads to the rest, they still need time to burn, they still need to be close enough to catch on fire, the ignite still needs enough damage to kill them in a single instance. Direct comparisons can be made to both "on death" explosion mechanics and to contagion (both in PoE1 and PoE2).

In the case of "on death" effects, they often do %hp damage, are instantaneous (or functionally so), and have fairly reasonable AoE. The only real requirement is that they need enough increased damage to allow the first couple to kill the next couple and so on. OK, so death explosions are strong in PoE, big news, they are generally limited by needing additional mechanics to activate if there are no readily available corpses.

Let's take a look at contagion then, it, being a DoT mechanic, is perhaps more directly comparable to ignite prolif. It's damage is largely inherited from other chaos DoTs, allowing the main skill to act in a more supporting roll, but requiring a second button press to do significant damage. It has decent AoE, which is more easily scalable due contagion not needing damage links and can focus on AoE and casting utility supports, as well as being a "spell" sourced effect it often has exceptional "spell area of effect" passives it can benefit from (the only tag that probably has an easier time scaling AoE is "curse"). Contagion's rate of spreading is also near instantaneous, since like "on death" effects, it happens when something dies, which only takes a little bit longer since contagion support DoT mechanics.

Finally, before we look at the problems with PoE2 ignite proliferation, let's remind ourselves of how it worked in PoE1. The damage was usually a non-issue, packs of mobs were unlikely to have enough hp or fire resistance to survive a solid ignite, besides maybe the occasional rare. It's base AoE was comparable to contagion, ~1.7-2m depending on gem level, if a bit more awkward to scale since it only benefited from generic increased Area of Effect as far as I am aware and did not inherit the tags from the skill that procced the ignite. Most importantly, though, it spread functionally instantaneously, but unlike contagion or "on death" effects, did not also spread from the affected enemies. In order to actually apply a new ignite and thus have a chain of ignites go through a pack, you needed Berek's Respite or Abberath's Hooves. In this way, ignite proliferation was more like Melee Splash or Shockwave support, allowing a single target mechanic to have limited AoE capacity within the same timeframe as it would usually have.

This brings us to PoE2 wildfire support, the functional replacement of ignite proliferation. It's damage potential is an entire new instance of the original ignite, with a fully refreshed duration as far as I can tell. This is fantastic, and puts it easily on par with contagion for ease reaching the benchmark of killing each mob in a pack, without the need to include another damaging skill. In the other two vectors of how I have been analyzing these mechanics however...well, it's AoE is a measly 1.5 meters base, 0.2 less than contagion's base without any of the ease of scaling, since it's hard to tell if it even scales at all without significant sources of generic increased area of effect, a stat that seems pretty deliberately lacking in PoE2 relative to PoE1. The real nail in the coffin for ignite builds though is the delay, a WHOLE 2 SECONDS of standing in that mediocre AoE for each mob. I understand that allowing ignites to spread like contagion raised some concerns about instantly igniting every mob in the map or igniting an entire breach encounter with a single button press (which honestly wouldn't even be as powerful as some of the things people are doing right now, but I digress), however, 2 seconds in PoE time, especially in PoE2 time where everything can and will kill you, might as well be 2 whole eternities. All this for a support that DOES NOT scale your damage, that does not function in most boss fights, that has a 120% mana multiplier, that is off-attribute for some ignite builds (many of the skills that need this support to improve their AoE are strength melee skills) and even though it is largely dysfunctional in most boss fights, is still one of the best supports for any boss fight with adds because ignite chance is now based on elemental ailment threshold, and does not accumulate over time, making ignite prohibitively difficult to apply for hit-based ignite builds unless they are half-healthing the boss in a single hit anyway (which seems a bit excessive if there was any intention for boss fights to last more than 5 seconds...)

While I know the team mostly just takes feedback and finds their own solutions, which I am generally in favor of, you are the ones with game development experience, not me, I would like to offer a few opinions on solutions. The first is really simple, just lower the time required to be near an ignite for it to spread (say 1 second instead of 2) and increase the base AoE (~2.0m instead of 1.5) as well as maybe allowing it to inherit attack and spell AoE from the ignite source (I don't think it does at the moment, though if I am wrong, then ignore that). The second solution I would consider is reverting it to the old ignite proliferation effect, allow the ignite to do AoE damage immediately to everything near it, and to burn enemies around the corpse, but not actually apply a new ignite to them (I don't really like this solution, because thematically it doesn't really feel like enemies are catching each other on fire, which is a major thematic win of PoE2's wildfire mechanic. If anything I think I would rather have a second support gem or a unique item with the PoE1 ignite mechanic as an option in addition to wildfire still existing). Third solution, copy contagion and "on death" effects homework, make mobs flare up and immediately ignite everything around them on death, or even just after a second or 2 of being on fire (this would keep the "wildfire" flavor of spreading from one to other, but might be too similar to contagion for some people's comfort, but people like contagion's spread method, it works, even if chaos skills probably need some damage numbers love in PoE2).

Love the game, but please let melee have smooth AoE, this is one of things holding it back and causing everybody to re-roll Spark and Herald of Ice...