Hi there.
The problem is that the numbers are BIG while “month”, “week” etc are small, so an eye typically catches numbers quickly and compares them.
On the screenshot it seems that the frequency is almost the same, while it’s not: 3 / month (1st) vs 2 / day (2nd).
Possible improvements  either some of them or altogether

Make different colors for year / month / week / day

Keep at least one number always constant, e.g. “per year”. So that people can compare numbers visually.

It is also possible to only keep numbers and show them like “12 / 1”, where the first number is average per year, the second is average per month. And make each number different color.
Alternative #1
Show 2 numbers:
25 messages
3 topics
Meaning there are 25 messages and 3 topics per month in average for a particular category.
Alternative #2
Considering this blog post…
“Because reading is fundamental”
http://blog.codinghorror.com/becausereadingisfundamental2/
…show number of hours people spend reading topics in a particular category besides the number of messages people write for the same period of time. E.g.:
25 messages
340 hours
Meaning in a single month people write 25 messages in the category and spend 340 hours reading (all readers summed up).