Why would it be a waste? People should finally understand, that difference between "branded" and "exact match" anchors from PBN does not make too much of a difference. People tend to use brand and URL anchors with shittier links and save exact and partial for PBNs, which is nonsense.
If you have 50 PBN links, all with exact match anchors, you would need good 4-5K (depending on niche) backlinks to have a good exact match anchor ratio. Stop overthinking anchors, use brand and URL anywhere you want. Impact on ranking is not THAT significant, especially compared to overoptimisation penalties that you can get if you overdo it.