ばかりだ・一方だ: the difference
ばかりだN3
Meaning
(Only) continue to, Keep on -ing, More and more
Past papers
Tested once in past papers
Example
彼は傲慢になるばかりだ。
He just keeps getting more arrogant.
一方だN3
Meaning
More and more, Continue to, Keep on, -er and -er
Past papers
Tested 4 times in past papers
Example
災害は増える一方です。
More and more disasters happen.
How to tell them apart
As a trend, 「ばかりだ」 is almost only for bad changes, rarely for good ones.
「～一方だ」 is also a one-way trend but works for both good and bad: 「悪化する一方だ」, 「回復する一方だ」.
If you see a good change like 「上達する」 or 「回復する」, pick 「一方だ」, not 「ばかりだ」.