Is my usage of “provided” and “but” grammatically errorless in this paragraph?

To conclude, I believe the adversities early marriage and pregnancy bring about, overshadow the rewards of it. This is, however, provided that a delayed action is not a result of mere procrastination or laziness, but a consequence of a justifiable and thorough preparation for a bright future.

Solution 1:

That seems entirely correct to me; however I consider as an error the omission of "so" after "This is". The cases of "this is so, provided" and "this is so provided" are found in plenty but there is not a single "this is, provided" (Google books).

It seems that what you would try to say is "that is"; this idiomatic phrase is complete in itself and not to be confused with "this is so" (ref.); if it is possible not to use a comma with "this is so, provided", the comma is always necessary after "that is" (OALD, ). Note that you can write, equivalently, "that is to say, however, provided that…".