Ok, I've had both a Quatix 5 & now a Fenix 7 pro solar sapphire.
The only real differences (other than preloads of software) are that there's a dedicated MOB button on the Quatix, and, as you say, connection possible to Garmin plotters.
However, really have to point this out bigtime, it's only Garmin Plotters & autopilots, and even then, only some of them. Not a huge issue for me, as I have a B&G system.
When it comes to the software, you can 100% load all the same software and it works just as good (or bad) as normal. My particular ire comes in for the Garmin Sail Race app, which has been programmed by someone who's never sailed before (eg, burn time only calculated while you're moving toward the start line (no use if you're beating up and down to try and actually burn time) and to set the start line, you have to port tack the fleet). 1000% use the RaceQs app - works great and uploads to the website easily.
So unless you have a full Garmin setup onboard, go the Fenix, which will be hundreds of dollars cheaper for the same models.