I mean, if you prefer untucked as a personal thing or whatever, just go with a shorter shirt. Tucked would still be the better option for the aesthetic you're going for, but at least a shorter shirt would look less waterfally.
On that note, I'm not sure your current shirt would look good untucked even without the blazer-- it's pretty long.
Sounds like I would have to get used to tucking my shirts in again.
Will your coworkers make fun of you if you tuck your shirt in? I don't really like tucking my shirt in either, but I think under a sport coat it looks better when tucked. At the very least, you should be wearing a shorter cut shirt. Or, ditch the jacket and go untucked.