FTL and Void War - When does 'inspiration' become ripping-off?

I touched on this in a recent thread, but thought I'd expand on my thoughts a little here. Void War was a featured game during the recent Steam Next Fest and it's developers openly claim that it was heavily 'inspired' by FTL, one of the most popular indie-roguelikes of all time.

It's the nature of creative works that people will inevitably draw inspiration from previous works. Terry Pratchett once compared Tolkein's effect on the fantasy genre to Mt Fuji in Japanese culture, saying that The Lord of the Rings was such a touchstone that its influence can be felt in all fantasy since, even if simply by deliberate avoidance. Clearly such creative inspiration is inevitable and in most cases it is acceptable to draw on previous works. However, I feel like Void War has crossed the line, and is taking as much as they can from FTL to build their game, rather than creating something original.

A simple comparison of the two games' Steam pages should indicate where I'm going. Almost every UI element from Void War is hard to distinguish from FTL, so much so that the game has previously been confused as an official successor or at least a well-made mod. The game has visually similar weapons, weapon effects, ship destruction, crew animations, UI placement, sound-effects and more, not to mention the fact that the game is also heavily inspired by Warhammer: 40,000.

Am I being unfair to think that this is too far? That too much has been taken from the original for this to be considered merely a 'spiritual successor' ? My gut tells me that Tundra are quite happy for their game to be mistaken for something as popular as FTL, especially with the developers moving onto other projects rather than developing a sequel.