Would it not be strange to accuse biologists of equinizing sharks because they say that horses and sharks are organisms ontologically on par with each other. Of course, both sharks and horses are organisms. Of course, they are ontologically on par. (If biological reductionism holds, they both reduce to particles. If biological anti-reductionism holds, neither reduces to particles.) And the similarities don't end there. They both have DNA, they reproduce sexually, they are both chordates, and so on. Nonetheless, they are obviously different in ways that do not mark an ontological difference, and the biologist is interested in such differences as well as in the similarities.
Eternalists get accused of spatializing time, because they are claimed to hold that time is a dimension ontologically on par with and akin to spatial dimensions. Now, first of all, an eternalist need not think time is a dimension ontologically on par with spatial dimensions. She could, for instance, be an absolutist about spatial relations and a relationalist about temporal ones, or vice versa. She could think that spatial relations are constituted by degrees of interaction (things that tend to interact more are therefore closer together), while temporal relations are primitive. Or she could think that spatial relations are primitive, while temporality is constituted by facts about the causal nexus. All if this is compatible with eternalism. So eternalists certainly do not need to take time to be ontologically on par with space. Of course, they will take time to be akin to space insofar as they hold that being now rather than then no more marks an ontological difference in an object than being here rather than there. But that's just one similarity, a similarity compatible with much ontological dissimilarity.
But let's even grant that we are dealing with an eternalist who thinks the temporal dimension is ontologically on par with the spatial ones. Still, as the case of horses and sharks shows, being ontologically on par is compatible with much significant difference. The biologist doesn't equinize sharks or sharkify equines. Likewise, an oscilloscope and a hammer are ontologically on par, and they are both kinds of tools, but saying that neither oscilloscopifies hammers nor hammerizes oscilloscopes. The differences are important and hard to miss.
The same is true for space and time. Persons' lives are strung out through time in a way that they are not strung out through space: they show significant temporal development but no analogous spatial development, and we are vastly thinner spatially than temporally. Time has a direction connected both with the increase of entropy and causation, while space is isotropic. Even in Relativity Theory, which treats space and time as a unified manifold, the temporal component gets counted completely differently in the metric: the square of the distance between two spacetime points in a flat space is equal to dx2+dy2+dz2−dt2: the time difference crucially gets a minus sign in the signature, a fact that has vast physical consequences. These are vast differences.
A standard four-dimensionalist analysis of change is that change consists of being one way at one time and another way at another. (It's hard to deny that this is necessary and sufficient for change1) This account is accused of making change be too much like the variation in landscape along a spatial axis. But that accusation assumes that on the four-dimensionalist analysis there is no significant difference between temporal and spatial variation. But if there is a significant difference between time and space, something that we saw is quite compatible with eternalism (and very hard to deny!), the accusation falls flat. Saying that temporal and spatial variation on eternalism is the same is like saying that there is no difference between imprisoning an innocent and a guilty person, because both are imprisonments. They are both imprisonments, but one is of an innocent and the other of a guilty person. Likewise, both temporal and spatial variation are variations, but one is a temporal variation and the other a spatial variation. Change is temporal variation.