You can't really compare the bug that was found in Core, which was theoretical at best, and fixed anyway before it even had a chance to do anything.
The Electrum bug as explained by theymos sounded as if you were just a click away from losing your coins:
This message is false, sent to you by a hacker. If you click the link in the message and install the software, then your BTC will be stolen.
When has Bitcoin Core had anything like that?
I wouldn't compare the two either, but the recent bug in Core was far more serious. It was "theoretical" in the sense that all bugs that haven't been exploited
yet are theoretical. Since you quoted theymos:
The bug fixed in Bitcoin Core 0.16.3 was really bad. IMO it was the worst bug since 2010. If it had been exploited in a 0-day fashion, significant & widespread losses (due to acceptance of counterfeit BTC) would've been likely, and Bitcoin's reputation would've long been tarnished. Furthermore, since a ton of altcoins are based on Bitcoin Core, this would've affected a huge swath of the crypto space all at once.
I encountered the Electrum attack. To be honest, it wasn't very convincing. It was a social engineering attack, not an actual vulnerability in the software. You would have had to open an external untrusted website, download the software, and also neglect to verify it. Plus, the malware only worked if you kept your Electrum keys online,
which isn't necessary.