Frankly I was kind of disappointed that the ending was a sacrifice of Allura, rather than a sacrifice of Voltron and the lions itself.
It felt like there was a recurring theme in the latter part of the show that Voltron had sort of outlived its moment, the new Robeasts had surpassed it. It was no longer the strongest weapon in the universe. Consider how useless Voltron itself was against the threats of the most recent season when it wasn't fused with the Atlas. It was powerful, but it had clearly fallen behind the curve.
So ending the show with Voltron going out with a bang, returning to the void between worlds from whence the comet first came, seemed like it would have been more fitting.
Alternatively: as a side note, was anyone else waiting for them to run into another universe's Voltron when they were hopping between realities at the end? I kinda had by fingers crossed for Voltron being outmatched alone, but as the problem escalated the big dramatic ending out be the Voltrons of multiple universes showing up to defend their own piece of the pie.