Blowing up planets costs energy though, it doesn't give you energy. Overcoming the gravitational binding energy of a planet is a huge power sink. That was one of Wildbow's bigger physics fails; I think he may have corrected it later to be a thing that's done to not leave any potential threats behind or aid in shard collection, but I don't have a citation on that at the moment.
Everything gets warped into absurdity if you try to peg Endbringers at a literal galaxy worth of mass each. An Entity mass on the order of a moon to a few planets makes a lot more sense for the scale of things we see them doing, the descriptions of their size while traveling which are large like planets but not blotting out galaxies large, the number of shards there appear to be, and the size of the shards.
Wildbow, while a good writer, isn't a physicist or engineer. When there's a conflict between descriptions and what makes sense and a number he gives, I'm personally going to go with something based on the descriptions.
If blowing up planets is a power sink (and they're not doing some exotic multidimensional mass-energy conversion shit to get energy out of it) then they kind of need to be that big though. Moreover the entities have no
reason not to be that big, given the amount of alternate worlds there are in the universe they inhabit. Using them all, or at least a large fraction of them, gives them more processing power, more energy, more
capability in general. They'd have to be dumb not to.
Furthermore, my personal interpretation of that is that they're moon-sized in any given 3-space, but obviously much bigger in total. (much bigger than a moon in any given 3-space would also make them too big to land on a planet, so that tracks) Also, this is the full entity, not the incredibly diminished Scion the characters fight. Also, his interlude explicitly states that one shard can be big enough to need multiple earths, so that alone makes an entity
much bigger than a planet, assuming they have anywhere near the amount of shards they're both stated and shown to have.
Interlude 26 said:
One shard is capable of settling in a grouping of near-identical worlds, drawing energy from all of those worlds at once.
I also don't see why the endbringers having a galaxy's worth of mass warps things into absurdity. They have the capability, in terms of reach, to access that much mass. I'd even go so far as to say a galaxy's worth of mass is insignificant to them. 10^80 alternate earths means taking just one atom from each of those earths gives enough mass to make an absolutely absurd amount of galaxy-massed endbringers.
The main counterargument against this sort of thing I've encountered is the fact Scion needed to ration his energy, but frankly, he was running on battery power. And he had enough of it to keep going for 3000 years of activity, when he only expected to need 300 years. Do you build a laptop with a battery lifespan ten times as long as you expect to need it? Not plugging himself into some kind of centralized energy storage or building a multidimensional mass-energy conversion reactor (or at worst, fusion) that could've kept him going indefinitely is a failure of planning, not of capability.
More than anything, in my experience with these sorts of arguments that go 'the entities aren't that big!', there is a failure to grasp the difference between the full entity and the diminished form that is Scion. Scion is not an entity. Scion is a few vital shards in a trenchcoat with a couple of multitools hooked up to a battery, responsible for running (his part of) the cycle and dealing with problems that arise. And even then he was only beaten when he
allowed himself to be beaten.
