As I don't use them, I wonder if you can combine the two? So that every source is contained and each destination is contained as well. Might get a bit annoying with somethings, but.

Yes, you can. I use both. My personal profile & work profile are different, and have different container settings.

I use profiles because I want state isolated for my purpose, not per web origin. So for example, I may need to visit google sites related to my employer's Gsuite, or my personal account used with GMail and phone, or as an anonymous user.

This also means that I have become somewhat resistant to scripted UI integrations. I don't really want my apps or sites calling willy-nilly into each other. I want _links_ which I can deliberately copy/paste into different profiles depending on my goals. E.g. do I want to visit someone's Google drive shared link as my personal account, work account, or anonymously so it doesn't pollute either of my drive UIs?

You could set BROWSER to a script which takes a URL on its command line, uses zenity to pop up a dialogue box showing it to you, with a button for each browser profile, then opens it in the selected one. With buttons for "Do not open", "Copy to clipboard", etc.

Just the dialog box with $1 should suffice. I do this on Windows. I can copy it to whichever appropriate browser, or simply dismiss it. I have my terrible source code somewhere on the Internet, but it should take less than couple femtoseconds for any HN readers to write their own, I suppose. I recommend everyone do this.

I have considered doing exactly this on many occasions but have never gotten around to putting it together - though I hadn't considered using Zenity.

I think a polished packaged cross platform app that does this would have some audience -akin to the intent dialogues on android & ios.

You could set BROWSER to a script which inspects the URL and dispatches to the right profile. This would be mildly awful but extremely unixy.