> These phrases in the context of writing, absent other context, have the same meaning. This isn’t really an opinion.

In a thread where others explain how to them, they have different meanings. It is quite obviously an opinion.

"In my opinion, an apple is an orange citrus fruit."

Your opinion may be true or untrue; it depends on what the meaning of "is" is.

Okay, but "surprisingly" has more possible meanings than "to our surprise", imo. How come you disagree?

Whenever a speaker is talking about opinion or emotion, it is the speakers' opinion or emotion unless otherwise specified or contextualized. If I say, "We should eat pizza," the correct interpretation is that it is my opinion we should eat pizza. If I say, "In my opinion, we should eat pizza," the meaning is the same.

Surprise isn't an objective fact. It's a statement of emotion or subjective experience or whatever you'd like to call it. It is often a consequence of an objective difference between an expectation and a result. (An expectation can be subjective, but whether someone holds that expectation is either true or false.) But surprise isn't that objective difference, it's the subjective response.

So if I say, "Surprisingly, the sun rose today," absent other context it means I find it surprising that the sun rose today. It doesn't mean, "Everyone should find it surprising that the sun rose today." For that, I would need to add more context or you would need to bring in some assumptions that aren't supported by my statement. So, this is equivalent to "To my surprise, the sun rose today."