I'm not wrong. There aren't any grammatical errors in any of the titles. As I said, you were just reading them differently, so you're seeing them as grammatical errors when they aren't.
There are many ways to render a Japanese title in a fan translation. It could be left in romanized Japanese, sure. It could be translated, or even given a fully localized title like "Legend of the Mystical Ninja." There are many ways to approach it, but there is no one way that it HAS to be.
Let's look at the title logo for Ebisumaru's game here:
Now imagine it rendered as a complete sentence. Would you put the comma in the box above Ebisumaru, even with heart after it, just to have it as a complete sentence? Would you remove the box on the top to make it look better as a complete sentence? Why insist that it must be a complete sentence there, anyway? It's not like there's an exclamation point after Ebisumaru.
You say that it's because the first game rendered it as a full sentence, and yes, it did... But look here:
There's no exclamation point after the name anymore. The title wasn't treated as a full sentence, unlike the very first game, and that was back in 1989. It separated the title logo into chunks.
How would you even render it as a full sentence with the 2?
Would it be "Go for it, Goemon! 2" or "Go for it, Goemon 2!" Both of those would come across as odd, and neither would work well with how the title is rendered.
You seem to insist that the entire thing has to be rendered as a full sentence because of the first game in the series... but even the Japanese developers didn't share that perspective. Why should the translations act like Goemon is part of a full sentence like the first game when the Japanese releases stopped doing that since 1989?
I maintain that the translated titles do not actually contain any grammatical errors. These translations, much like every Goemon game since the second Famicom release stopped treating Goemon's name as the last part of a full sentence.
But if it's any consolation, if I ever translate the very first entry on the Famicom or the MSX, I would definitely keep it as a full sentence, just like the Japanese game does, and put "Go for it, Goemon!" on the title screen, with the comma and the exclamation point there.
As for Tengai Makyou, I chose to leave Tengai Makyou romanized rather than translated due to the lore surrounding the game, to delineate the difference between "Far East of Eden" and "Tengai Makyou," which is explained in further detail in some of the manuals. (I haven't translated them yet, though.)