I think you're not remembering the amount of silliness on previous shows, let's analyze TNG S2:
Serious Episodes 59% (13 episodes)
- "Where Silence Has Lease"
- "Loud as a Whisper"
- "The Schizoid Man"
- "Unnatural Selection"
- "A Matter of Honor"
- "The Measure of a Man"
- "Contagion"
- "Time Squared"
- "The Icarus Factor"
- "Pen Pals"
- "Q Who"
- "The Emissary"
- "Peak Performance"
Not Serious Episodes: 41% (9 episodes)
- "The Child" (Troi's immaculate space-conception)
- "Elementary, Dear Data" ("Holodeck gone wrong" story)
- "The Outrageous Okona" (Data learns comedy)
- "The Dauphin" (Shapeshifting monster princess)
- "The Royale" (Another "holodeck gone wrong" story with no holodeck)
- "Samaritan Snare" (We are smart)
- "Up the Long Ladder" (Space irish)
- "Manhunt" (Lwaxana Troi is on the hunt for a husband)
- "Shades of Gray" (A clip show)
I think it's a good proportion of silly so far...
e: I made the same analysis for TNG S3, and I could only identify 3 silly episodes, so, I don't know. Take this with a grain of salt. Maybe SNW S4 is all business.