I have seen many of those spider flags around and it had me thinking if all the effort you put in summoning the first boss is actually a big waste of time, for instance why not to give people who kill the boss more...efficient things, such as: Insta/almost insta taming-sounds fair as it can help you spend less time with the taming and keep the efficiency up or just get you this new high lvl dino you wanted to tame so badly but never had the time/kibbles for him, "special" resource that can drop only from this specific boss and give you access to more points for engrams which is great as you can make bosses in different measures of difficulties the harder the boss the more points you get for even more engrams, this one is more interesting: a supply drop that only if you killed that boss you can actually open it, another idea was to give you a "pet" or even ride-able dino as a "gift" from the boss(can even make a cute story of how it got eaten and lived inside the boss for a long time), incubation machine for an egg!- so you could hatch one or many eggs into dinos but if we go by the only one dino maybe the hatched dino will be special: high lvl when hatched/a VERY good stat/unique colors scheme/etc...
I am writing it down because spending tons of time to get those artifacts is hard (especially in a small/not very active tribes) even in big tribes it is still hard and a damn flag is not the thing you deserve for all the time you spend getting those artifacts.
so in order to sum up I believe that people who actually worked hard on getting those artifacts should get much more than just a flag with a spider mark on it.