In the following sentence:
正如我们之前所说，Alphabet在企业投资者中似乎有些另类。
I assumed the usage of 所 in this case is, according to Pleco:
[as a noun without 的, esp. when the verb is monosyllabic]
据你所说
But in this sentence there is no preposition such as 据. The whole sentence would work fine even without 所 I think.
So what does the 所 work for and what meaning does it have, compared to the case where 所 is not used?
正如我们之前(说)= Just as we (said) previously- 说 is a verb here
正如我们之前(所说)= Just as (the words) we (said ) previously
"我们所说" is short for "我们(所)说的話" = "the words (that) we said"
therefore, "我们所说(的話)" is a noun
When you say "正如我们之前(说)" you have to follow it with a quote of what was said
When you say "正如我们之前(所说)" you can follow it with a quote of what was said or omit it and presume it is known
ABC
所
CONS.
1 ~ V de that which
我所说的（话）
what I said
So if we want to get into semantics I think that 我所说的 would be better put as: the things that I said, especially looking at ABC's definition.
Like you said, taking away 所 would still be valid: 我说的 but that would just be the difference between what I said (我说的) and the things that I said (我所说的).
Now coming back to 据你所说.
ABC
据
CONV.
according to; on the grounds of
据他说...
According to him...
but if we add 所: 据他所说的 now becomes: according to what he said.
所x is referring to the object of the verb x, and makes the phrase nominal.
e.g.:
＂汉语８００虚词用法词典＂所二，用在做定语主谓词组的动词前面，表示中心词是受事 used before the verb in a subject-predicate structure to make it passive (applies to #1)所＋动词／动词词组＋的＋名词／名词词组（１）我所认识的人中没有叫彼得的。（２）我把自己所想到的几个问题都说了，希望大家商量一下，看怎么解决。（３）我们所提的意见和建议不一定对，希望领导考虑吧。（４）现在，大学生们所关心的问题主要是毕业以后就业问题。（５）现在群众所关心、所议论的热点问题还是教育改革、医疗改革和住房改革问题。（６）一些留学生给学校领导所提的这些意见和建议，学校领导一定会认真研究，然后给大家一个满意的答复。四、用在动词前面，跟动词组成体词结构used before the verb to form a substantive structure (applies to #2) 1.所＋单音节动词（１）来了四五个学生，我包了一百多个饺子差不多都吃完了，所剩无几。（２）今天是自助餐，大家随便吃，各取所需（３）所说那里不错，我们就去了，结果大失所望（bkrs:greatly disappointed）。（４）传说这首诗为大诗人李白所作，其实不是。（５）随着经济改革的成功，政治改革就是大势所趋，人心所向（６）看人不能只看他怎么说，还要看他怎么做，从一个人的所作所为，就能看出他到底是个什么样的人。（７）如这篇文章所说，一个人做点儿好事并不难，难的是一辈子做好事，不做坏事。（８）他视金钱如粪土，你说做官是受苦，真是英雄所见略同（bkrs:have similar views）。
