First, we do not know exactly how rich Solomon was. And even if we did, comparisons with those who have reigned since, even into modern times, are fraught with difficulties due to inflation, vast differences in economies (agrarian vs, say industrial, etc) and the way wealth was counted and evaluated.
It is also difficult to know on what basis Solomon was regarded as wealthy: Was he wealthy compared to the average citizen; or, Did he own a significant part of the total wealth of the land such as farmland, or gold, silver or just land and cattle, (eg, Job) etc, etc? There are many ways to measure wealth.
That Solomon was vastly wealthy is beyond dispute on almost any basis, even if direct comparisons with other monarchs are impossible.
However, it is possible to make a few remarks about the two quoted texts:
- 2 Chron 1:12 says that Solomon was richer than the kings before him and after him. If this refers to all the kings of Israel and Judah, then the statement is not difficult to believe.
- 2 Chron 9:22 says that Solomon was richer than all the other kings of the earth. If this refers to all the kings of the earth that were (at least approximately) contemporary with Solomon, then, again, it is not difficult to believe.
How much more than this we can say, is not known. The language is very carefully worded and is significant for what it does not say. For example, it does not say that Solomon would live the longest (there were others that lived and reigned longer); and, it does not say that Solomon was the richest king who ever lived.
Therefore, to be safe and conservative, it better to confine one's understanding to above two statements.