Ingress: Softbank ultra links vs. shields

Here is an attempt to answer my own question: Looking at the "Portal Defense Boost % based on Number of Links" picture in https://gaming.stackexchange.com/a/133484/100574 , the defense boost provided by links is always below 60 (at least for portals with <=10 links). Assuming that an ultra link just adds 50% extra to this, the extra mitigation provided by an ultra link should always be less than 30. If this is right, even a common shield (mitigation 30) would always provide better protection than an ultra link.

(Since I am unsure whether I understand the referenced answer correctly, I would be happy to receive alternative answers from people who have some actual knowledge about this.)