I found the Mariners' schedule/broadcast info here, but looks like other teams (via a search) are also covered:

https://www.cabletv.com/sports/watch-seattle-mariners

So unless one's a super-hardcore fan, someone who only wants to watch their local team can just get the in-market package, throw in an antenna (for NBC/Fox, including the World Series) and just listen to the remaining 7 games on the radio (or skip altogether)?

Again, when it comes to streaming, sports are generally a rip-off... the only question is how much of one (and how much one's willing to pay).

This year, MLB also offers a subscription package of in-market blackout-free streaming for most teams, separate from MLBTV (though the two also can be had as a bundle).

As ESPN is now handling MLBTV, they're trying to force new subscribers to get ESPN Unlimited when signing up (though that can be cancelled right away).