Our alliance had a spreadsheet keeping track of the bonus damage values people were getting on their Kuva weapons. Sadly I can't find it anymore, but here's an early data summary I did manage to find:
25-29%: 43 entries (36.8%)
30-39%: 31 entries (26.5%)
40-49%: 20 entries (17.1%)
50-60%: 23 entries (19.7%)
Looking at the data linked in the post above, the distribution is very similar for both data sets. The bonus damage values are definitely heavily weighted towards the low end. While this data is for Kuva weapons, the Tenet ones are almost certainly the same.