Thanks for the question Peter!
Simple math would suggest 30mg / 7500mg = 0.4% withanolide per tablet, which seems low.
However it is a very high dried root equivalent of 7.5 grams. If you look at other brands, they may have 600mg KSM-66 with 5% withanolides which still provides just 30mg per capsule, the same as yours. Or they have 300mg capsules at 10% withanolides, again 30mg. We have just seen that Jarrows has an even lower amount, 300mg capsule with 8% withanolides yielding 24mg.
So it sounds like your supplement is fine! Our best guess is KSM-66 Ashwagandha simply comes in different strengths / potencies / dried herb equivalents.
What brand is if it you don't mind us asking?
Further research since I posted the question and I discovered that if the product is KSM-66's variety of withania somnifera, then 5% of each mg = the active withanolides ingredient.
So if, hypothetically, the optimum dose of withanolides is 30mg day, then 600mg KSM-66 daily achieves that goal; 600 x 5% = 30mg withanolides.
The supplier I purchased from told me the 7500mg dried root refers to the volume used to extract the 600mg tablet. So each tablet contains 30mg withanolides.
The supplier I referred to in the original post is Curoso's Ashwagandha (KSM66). https://carusosnaturalhealth.com.au/ashwagandha
The other ashwagandha I bought was Nature's Way (KSM66).