I first saw this movie on TV and immediately thought that this was WAY to similar to Voltron versus the RoBeast of the week, especially when the Gypsy Danger sliced the monster cleanly from stem to stern.
Voltron is basically an American adaptation of various old classic Japanese mecha (giant robot)-themed animes...the American company that created this Voltron series basically took numerous different old Japanese mecha-themed animes and then dubbed them into english and released them as part of a series that they named "Voltron".
This classic mecha/Kaiju genre is very popular in Japan and has been used in many forms of media such as animes, movies and TV Shows in Japan since at least the 1940s. The director and creator of this movie Guillermo del Toro is a huge fan of this classic japanese mecha/kaiju genre and he took inspiration from the many old Japanese mecha/kaiju style animes, movies & TV shows he had watched growing up. Which is why you see alot of similarities between this movie and other Japanese mecha/kaiju-theme shows and animes like Godzilla, Evangelion, Ultraman, Gundam, Mazinger Z, including Voltron (which is basically an American version of various Japanese mecha-theme animes) etc, they all fall into this same classic mecha/kaiju genre. Because this movie basically uses many of the same styles and concepts and ideas that are usually used in this type of genre.
You forgot Tranzor Z. I think I'm the only person who remembers that show. But Voltron was the first mainstream cartoon to show a giant robot batteling giant monsters in the US. It made a big impression. Plus the lion robots that joined together to make the robot was just flat out cool. The toys were awesome.
It sure brought back some good memories watching voltron as a kid. I had the theme song in my head when gypsy danger's giant robot head combined with the body.