Probably most of this stuff is from PCV valves. Probably part of it is oil from valves guides.
I did breather reroute and I'm planning use cleaning fuel additives time to time so I hope it will not be so bad. I also cleaned injectors so it should spray on the valves better.
I think the most significant cleaning result was from Seafoam spray and CRC valve cleaning spray I sprayed in the intake before. I used Seafoam fuel additive and did not see big difference. I also used Gumout fuel additive recently and probably it helped loosen the dirt so it was coming off easier while sandblasting.