Here's a good article that covers the advantage of the HSA and letting it grow. Unfortunately, we haven't been doing this for 20 years as in the example but our current balance is almost half the example amount since we've both been able to contribute.
https://www.thebalancemoney.com/max-out-your-hsa-contributions-4157954
Let’s say that the maximum contribution never went up, and you contributed the maximum for an individual each year ($3,850) for 20 years and you earned a 4% rate of return.
We’ll use a very conservative return rate because you'll have some years where you'll have to withdraw funds for medical expenses. Using these numbers, you would have a balance of nearly $124,000 that is completely tax free if it's used on qualified medical expenses.