Both, since browser these days don't even show the number of connections and download speed for a loading page, much less an indicator for high CPU usage. I'm not saying displaying this stuff would be enough by itself, but hiding what is going on just so we can have a slightly bigger viewport into unicolor surfaces with huge padding and line spacing certainly doesn't help.
I know there are all sorts of flags etc, but consider old Opera, where switching the status bar between none, simple and advanced was right there in one of the main menus. That was a good start, that stuff would be compact and super useful by now if we'd just keep going.
F12 has becomes something of the universal key for Dev Tools in the browsers. It's not compact, but it is super useful and does have all the information and more. Most browsers even offer Profilers to get detailed stats on CPU and Memory usage.
Sure, it doesn't explain to average users why the webpages they view might be slow, but average users don't care.
Average users don't care about encryption either, yet we still have the padlocks for those who do. More importantly, average users are not creating browsers, and the people who know better can't hide behind them.
The average smoker probably doesn't want to hear smoking is unhealthy. Does that mean doctors should adjust their advice respectively? At what point does "professional" really mean nothing other than "gets money for it, like a carpenter or a thief or a drug dealer might"?
We don't even have the right to "just give people what they want without any judgement on our part", but we certainly don't have the right to ignore those with legitimate concerns because ignorant or apathetic people are more in numbers. That goes for everything, everywhere. That goes to how you are supposed to look out for little siblings when parents are away, and it goes for expert knowledge or intellect.
"This website is running long running scripts", "This website is not responding": those are already equivalents to the smoker warning that show up from time to time.
But what is any user supposed to do with a blinkenlight telling them what they already mostly know: that a website is bloated/slow/eating their machine slowly? If there was an alternative website, maybe they'd already be using it. If they thought complaining to the site's owners about it, maybe they already had or are already aware that they'd be shouting into a careless corporate void. That mostly just leaves uselessly blaming their browser for a blinkenlight that tells them something they already know and can't care about.
I know there are all sorts of flags etc, but consider old Opera, where switching the status bar between none, simple and advanced was right there in one of the main menus. That was a good start, that stuff would be compact and super useful by now if we'd just keep going.