I guess, I have to be online all the time, or?
And generaly I think, that a stand alone program is always
faster than a Browser App...
You can use Construct 3 offline. I believe you have to authenticate your account online at least once a week though.
You also may have a misconception about an "online" app where everything you do needs to be processed on a remote server, which then needs to respond and you have latency issues. Construct 3 is a browser app, but it runs entirely on your own computer.