Past tense and ~と思う

Question

In my grammar textbook, there's the following fill in the blank:

報告書はこのような書き方では（　　）と思います。

One of the incorrect choices is

報告書はこのような書き方では（わかりやすかった）と思います。

Incidentally, the correct answer is

報告書はこのような書き方では（わかってもらえない）と思います。

However, I'm struggling to understand what is incorrect about the first sentence. Is it grammatically incorrect to have a past tense phrase before ~と思う?

In my googling, I couldn't find a definitive resource that answers this--all the examples were extremely basic and only used present tense.

In English, there is a slight nuance between

1. I think it is easy to read. (I currently think it is easy to read.)
2. I thought it was easy to read. (In the past, I thought it was easy to read, but that may not be the case now.)
3. I think it was easy to read. (I currently think it was easy to read in the past.)

All of these are grammatically correct.

If the first sentence is indeed grammatically incorrect, how would you express these separate concepts in Japanese? Otherwise, why else is the sentence (semantically) incorrect? There is no other provided context, by the way.

Answer 1

このような書き方では（わかってもらえない）

「（こんな/このようなetc.）XXでは」 is usually used with a negative word or a phrase with a negative meaning.

◎このような書き方では、わからない。
◎このような書き方では、わかりにくい。
◎このような書き方では、わかってもらえない。
✖このような書き方では、わかりやすい/わかりやすかった。

To use わかりやすい/わかりやすかった in your sentence, you'd need to replace では with なら.

◎このような書き方なら、わかりやすい。
◎このような書き方なら、わかりやすかった。

「報告書はこのような書き方ならわかりやすかったと思います。」
"I think the report would have been easy to understand if it had been written this way."
「報告書はこのような書き方ならわかりやすいと思います。」
"I think the report is/will be easy to understand if it is written this way."

Answer 2

If you take out the は (報告書はこのような書き方では（わかりやすかった）と思います -> 報告書はこのような書き方で（わかりやすかった）と思います) this would be the correct expression. Essentially means “I think the report is easier to understand if it is written this way”

報告書はこのような書き方では（わかってもらえない）と思います。Essentially means “I think the report would be misunderstood if it it is written this way” - misunderstood being the past tense here.

But I could be wrong here - anyone else have any thoughts?