We've indeed discussed that. But it's not an issue of whether you should have cool stuff as a result of successfully leveraging rare resources. It's an issue of whether the specific cool stuff you've gained is something that should have been available to you.
Here's the thing: in a simulationist game, whatever ability you have, NPCs with similar power levels and/or resource access must naturally have abilities of analogous effectiveness. If you live in a world where a chūnin-ish summoner can get an ability that lets them automatically ignore an attack that would cripple a normal ninja, then that means you live in a world where anyone of similar resourcefulness can get, say, an ability that lets them automatically inflict an attack that would cripple a normal ninja. In other words, if you've obtained a poor man's Earth Spear with your resources, then other highly-advantaged new chūnin out there are walking around with a poor man's Rasen-Shuriken or a poor man's Mangekyō Sharingan. Such a world is a lot more lethal than the world you thought you were living in.
So, I think the strongest argument to keep PC and the other Pangolin jutsu is as follows:
Summoners aren't normally terribly useful to their summons. Summon clans care about their own path, and don't care too much about the human path. In fact, sometimes, summoners are detrimental to the clans (see: the crow stuff). It also provides an additional way of secrets leaking to their enemies. As a result, while Summon clans are happy to be summoned by summoners, and appreciate another small way to interact with the human path, it normally doesn't matter. Additionally, as they have few ways of directly influencing the human path, it is difficult to protect secrets. So, normally, they don't give away secrets to their summoners, as the risk of other clans' summoners discovering their techniques is unacceptably high, especially for a world which works off a much slower time-scale (where individuals live for centuries rather than decades).
This is significantly different for the Pangolin tribe in particular. They now have a summoner who provides outside context solutions to problems within their own path via sealing. Additionally, due to their isolation in the summon path, they have a limited number of solutions without appealing to dangerous and risky methods, such as their secrets being discovered by other summon clans due to propagation of their techniques on the human path. That said, they are building towards an endgame in their war - Skytowers are a huge advantage to them, as demonstrated by how it allowed them to enslave a clan within a year or two. Additionally, they expect that if they keep Keiko and her friends alive and safe (via strong techniques) they will be able to receive additional, new, war-changing inventions before the other summon clans.
All this means that they *are* willing to trust their summoner with their most forbidden secrets because they're getting new forbidden secrets in return, secrets which have allowed them to rapidly expand their empire. This almost never happens, as atested by the relatively few "total change in how warfare works" events there have been in the past. The Pangolins wish to maintain this superiority as long as they can, which means keeping Keiko and friends as safe as possible for as long as they can provide the Pangolins new seals. As this has a strong chance of winning them several wars within the next few decades, it's worth the significant risk of leaking secrets to their enemies over the next couple centuries.
As a result of the above, most clans keep their techniques, or, at least, their very best techniques, away from their summoners. This means that the human path is relatively unchanged as a result of the Pangolins choosing to give away their crazy powerful abilities to Keiko. Additionally, it means that enemies of the Pangolin clan, if they saw both the skytowers and the fact that there is now a Pangolin summoner would likely gun very hard for Keiko's death, as it would be a significant detriment to the Pangolins. So, I don't think this would increase the deadliness of the world at large per se, since most summon clans wouldn't give out secret forbidden techniques, but *does* increase the risk that random summoners begin targeting Keiko (thus increasing the rate at which we will encounter people with esoteric and dangerous abilities).
