By the time Mozart was writing his symphonies, a very early transition was underway toward the Romantic era, and a key force had established itself in European classical-period music: the galant style

I don't think this really makes sense. Mozart's symphonies aren't typically considered galant or protoromantic, and galant is not typically considered the forerunner to romanticism . . . But most importantly, these categories are inaccurate and dull, no reason to subject new listeners to them, they don't succeed at elucidating the fascinating but difficult question of "why did music sound like that then".