"Would be nice if you could press digital crown or side button to make the timer stop"
Yes - THIS! This would solve the issue and make the watch 1000x better as a fitness watch.
Although it still won't solve the problem of the fitness app randomly stopping its recording - which mainly seems to happen in the rain because the touchscreen is getting confused as wet clothes touches against it. I've had that happen in Strava, Runkeeper and Runtastic. The solution is covering it up completely - which is not exactly the point of taking it running in the first place!
IMO Apple needs to figure out these issues with its touchscreen if its going to be taken seriously in the fitness watch space