Since I have GMail, I'm not worried about clicking on spam. I know I trust what I get, and the exceptions I don't have to click.
My problem is exactly the "load external content from individual senders" matter.
You have to do it for every single sender.
It will bloat your contacts list. (I'm not using it... but are 100 noreplys really deserving of contacts list entries?)
I'm not saying loading external content is a good default.
Privacy in Vivaldi is an option - and convenience is a valid choice. I'm not worried if a substack email knows who I am.