It's a fair point that hackers do tend to need bigger dice pools because of the need to succeed on more tests than the gunbunnies need to succeed on to win a combat.
Still, whether you can't be seen with 16 dice or you can't be seen with 20 dice or you can't be seen with 24 dice, the Host goes on alert at GM's whim/discretion anyway. It only takes one hit on an unopposed (i.e. your dice pool is irrelevant) perception test to know there's a silent running icon in the host. BAM that's potentially all it takes for a GM to say the whole damn facility goes on red alert, if he's got a mind to.
Edit: I kinda like running NOT silent when I'm hacking a host anyway. You can't get in if you don't have a mark, so as far as the Patrol IC is concerned you're legit. But again, until such time the GM decides "no, the host goes on alert now" so fundamentally it's no different than running silent. Only you don't suffer the -2 dice penalty
Ditto, but that all depends on the Host. Most Missions seem to have ghost towns for Hosts so hackers stick out.
And a Hacker should be in and out of a Host pretty quick. In, find the thing, hack the thing, leave. If your plan involves hacking several things in a moderate to high rating host, you need a new plan. Even a Rating 5 host is tossing 12ish dice and will potentially run your Overwatch score up fast.
If the GM decides the Spider or IC does the "Check for Silently Running Icons" every few Seconds... yeah, the Host is going on Alert. Absolutely nothing a PC can do about it, which is why GMs shouldn't do that and should be using the Data Trail chart on p. 86 to search specifically for the Hacker with an opposed Matrix Perception roll. And also because the "Check the area for Silently Running Icons" is a hot mess of a rule and should be ignored, and the standard Matrix Perception Action should be used in all cases.