Back when Chrome was new, you could run Firefox with a decent selection of add-ons to get security benefits of similar magnitude through different mechanisms. The NoScript extension was at the forefront, providing a lot of functionality way beyond just blocking JavaScript per domain. And Firefox with extensions always had better privacy controls.
You can make your arguments about noscript if you'd like (I have a great respect for the project) but I think it was essentially irrelevant to user security at the time, real users were really harmed by malware that exploited Firefox, Java, and Flash, and Chrome killed every one of those attack paths in virtually no time at all.
Computers were far more dangerous before Chrome. You watch old TV shows and it's a joke that people would visit a site and get hacked - that's unrecognizable today, it simply doesn't happen. It used to, Chrome changed that.
This is true, but this is why we create faster and faster PCs, so our software can do more. The cost was because you were getting new safety features. Want the app to be fast, able to show you lots of tabs with no delay? That takes RAM and CPU. The CPU and RAM are there to be used for features the user wants. It's actually 100% ok if a computer has to work really hard to run an app as long as that app is designed well, it means the user is making it do lots of useful work. That's what the computer is there for.
I think you accidentally responded to the wrong comment, I didn't make any excuses or debate tradeoffs. I said "things have costs".