I wouldn't call GoseiRed vulnerable at all. He was a courageous, determined, focused and skilled Red.
The problems come when he turns into Alata.
Alata creeped the hell out of me. Always cheerful, always optimist, always friggin' smiling! Reds are supposed to be the ones to keep the team's morals high and even inspire them, but Alata turned it up beyond the scale that he crossed the uncanny valley and creepied me out.
I liked GoseiRed a lot, but Alata made me cringe. It's like they were two completely different characters for me and both in the opposite sides of the likeable balance.
I enjoyed Goseiger quite much, but I must admit that for me the bane of Goseiger was its terrible cast. And don't mean it only in terms of looks, they were terrible actors which coupled with poor characterizations from part of the guionists.
And MagiRanger was a series the majority of people liked. Was it perfect? Far from it, but it was enjoyable and its elements worked well together. It has its faults, sure, but it's still a solid series and I find it one of my personal favorites (it's obvious).
And that "magic doesn't fit with Super Sentai" is so... erm... so stupid argument that I don't know where the hell you heard it and I won't even comment it.