I don't hear it as softer at all. As sounds go,
Rowena seems pretty close to other -een and -eena names which we are all pretty used to. And that abrupt -enna just does not appeal. Maybe I'm too used to the
Rebecca +
Rowena pairing in, er, Ivanhoe I think.
I quite like
Rowena, but I prefer
Rowan on males. And I don't like
Ronan at all.
Morwenna is somewhat OK but - like Rowenna - sounds heavy and clunky.
A friend once met a woman named
Owena and said she'd assumed it would sound like what it was:
Owen with an -a ending. But it sounded like
Rowena without the R!