So, there’s a long-extant ticket to improve the user experience here at least a bit.
Currently, the plan is to make the designer ‘remember’ your last selection, at the very least - so if you last made a flex container, as long as you keep your designer open, the selection will default to flex.
Longer term, we want to move more “stuff” like this into a designer attached property store/configuration, that persists across restarts. There’s lots of complications there, though, so don’t expect it in the short term. However, I did kick the existing ticket to make this dialog ‘remember’ your last selection up in priority based on this thread + the ideas post linked.