Spotify streams really don't mean shit. You need more info than that to compare bands, like location for example. French and Dutch bands will obviously be bigger in Belgium than in the USA. If Gojira is not popular in the USA then their Spotify streams will be a lot lower, but it says nothing about their popularity in Belgium.When did Gojira become such a global headliner? Spotify has them with 2m listeners, that's not..... much. Ice Nine Kills has more and they don't headline anything. Marilyn Manson has 4 times as many and still would not be one of the two headliners.
I mean they're fine, but neither are they huge nor a long lasting cult band like Machine Head. The Olympia performance didn't turn them into the next Judas Priest.
Even before the olympics thing they were already headlining Graspop and Hellfest, but obviously it made them even more popular.
Gojira is indeed no Judas Priest, because Gojira as a band is still increasing in popularity but Judas Priest is not. Obiously they have the legacy status and nobody can take that away from them, but they are by no means an up and coming band.