[2024] What's the idea behind Cryptobloom? Why a healing AOE effect on an Offensive Magic Pen item?

Cryptbloom was designed as a Void Staff alternative. This led down a pretty linear path:

1. We don't want an item that does more damage than Void Staff, so it probably should have less pen and/or less AP.
2. We can give it other stats if we want to fill out the stat profile. Haste makes sense here since by the time I was working on Cryptbloom I knew that there was going to be slightly less haste in the rest of the system (no mythic passives, nerfed haste boots, no 30 haste items, etc.) and we were willing to accept AP champions getting some of that haste back with a damage tradeoff. But HP was also something I considered, though I never actually tested that version.
3. In keeping with #1, we want an effect that doesn't provide any damage, because we don't want this to compete with Void in terms of raw damage output. It also probably shouldn't be pure stats since that's what Void is, so it wants some kind of unique effect. Given the above reasoning, it should be some type of utility effect.
4. One of the major concerns with the AP items at this point was that the new AP system was adding a lot of damage and removing some health from the primary build paths for a lot of champions. So, if not HP on Cryptbloom, then maybe some type of conditional survivability.
5. Given we're looking for some kind of conditional survivability and/or utility, what users do we want to target? Well, there's plenty of AP champions that like getting AP and Haste but have parts of their AP ratios in utility that don't scale with %pen and therefore might be inclined to give up some %pen in place of utility (Sylas, Seraphine, Orianna, etc.). So from the pool of champions we were looking at, some kind of team utility made sense, particularly since any place we can reward typically selfish champions for buying something they feel good about that also benefits their allies (e.g. Fizz/Sylas/LeBlanc/etc. buying Cryptbloom) is a huge win, and many of the other potential users in this space (Orianna/Karma/Seraphine/etc.) were already naturally disposed towards that kind of effect.
6. So, I originally tested something very similar to Fiora's ult on takedown (scaling with AP and all that of course). This tested well for the more selfish melee users like Sylas and Akali, because they would normally be on top of anyone they were fighting, but the ranged users were unhappy with it. Also, sometimes allies wouldn't be happy with feeling like they were losing out on value if they left the zone to chase kills or whatever. So I tried a few iterations, one that spawned a rectangular zone that extended from the enemy body to the Cryptbloom user, one that spawned a bigger circle directly between the enemy body and the user, but asking allies to stand in a zone for a few seconds to get the value got old pretty fast as a mechanic that would trigger very frequently in teamfights. So I tried the healing nova version (using temp VFX that was a modified ASol shockwave), and that worked pretty well for getting the heal to everyone without occupying mindshare (mindshare wasn't a huge concern but we didn't want to make it something that would be massively more complex than Void).
7. Later, I pushed Void as a more expensive slot-efficient item and Cryptbloom as a cheaper spike, though I ended up going a little back on that later in development. It's possible that pushing their costs further apart would get better differentiation (buy Void when you can afford it as a more powerful, harder to access spike vs. the more consistent Cryptbloom), but I think the current version of the system works reasonably well despite their costs being close together.