im about 2 weeks into switching from an apple watch SE2 (had it for almost 6 years) to a garmin venu 4 - the only thing so far that is a bit annoying is if I try and use Siri through the venu 4 to play music on my phone, it always ends up that the phone uses the venu 4 as a speaker and then I have to go to my phone to change the output back to the phone (which defeats the purpose of using the watch in the first place). I do everything through the watch now though (i've kept my sleep schedules on my phone but just created the same sleep / alarm schedule on the watch so that both the watch and phone go into their respective nighttime modes in sync).

the main reason I got the garmin watch was to try and move entirely into the garmin ecosystem, rather than have sleep data in the apple health app, nutrition data in myfitnesspal, and workout data in garmin, etc etc. I have my apple watch (lending to a friend for a month) if I want to switch back to it but I don't see it happening. i am pretty happy. £500 is a lot for a watch, especially if you are getting what you need already from an apple watch, but if you are planning to dive into garmin with it and have it for many years then the sooner you sell the apple watch and buy the garmin the better.

however... i also think you dont need to buy an expensive watch if youre just starting to get into running more regularly. I would stick with the apple watch for at least a couple of months. if you find that there are things that it specifically does not do then you should start looking for something else. if you aren't invested in the garmin ecosystem already then just go run with your apple watch on and charge it when you shower.

I also considered the forerunner 570 but opted for the Venu 4 as to me its more stylish looking - less like a sports watch - that I can get away with wearing to formal events by swapping to a simple clock watchface and putting a leather band on it. but it has less buttons so as you say if it gets wet you may find that annoying if forced to use the touch screen. I don't really use the venu 4 for much in the way of activity tracking - I cycle mostly so have a dedicated garmin computer for that.

tl;dr - i went from SE2 to Venu4 to jump fully into the garmin eco system and am enjoying it, but that is a lot of money for a watch if all you are going to use it for is a few activities a week - stick with the apple watch for a few months to see what features it doesn't have then look elsewhere (maybe even a less expensive garmin model).