Web browsers is one of the most popular attack vectors and they are riddled with even more attack vectors by third party software like all kinds of addons.
Using the web browser as a base for a wallet is dangerous imo.
And using a third party website to store your wallet is even worse. MT.GOX and countless of others have ruined people that thought it was a good idea.
As it’s the official recommended wallet I think it actually hurt Cardanos growth badly. There is not a single setting in this 300mb monstrosity.
How are Cardano going to grow into a big decentralized system when this is the main wallet people have to use? I don’t see it happening.