There are no quotes regarding the number of ranger spells known.
At least, I couldn't find any.
The developers consider spellcasting a key source of the ranger's power
My favorite developer intent article says the following about ranger spells:
Rangers have a spellcasting progression that is half as vigorous as the normal progression. The Spellcasting feature can be tinkered with a bit, but it still needs to be a significant portion of what the class can do.
Much of the ranger’s extra potency in combat comes from spells such as hunter’s mark and from the class features granted by the ranger archetypes.
It's clear that the developers envisioned spells being a core part of a ranger's power, and that specific spells make up most of that power. Thus, for the ranger, it seems that the total number of spells known at level 20 is not correlated to the intended strength of the ranger's spellcasting. Instead, it's the ranger-specific spells that make up the ranger's strength.
Now, that's just the developer intent at the time of the class's creation. The existence of a UA Revised Ranger shows that the developers eventually came to believe that the Ranger in the PHB was too weak:
As such, the ranger’s status as a sore spot for
players has been a cause for concern for a while.
Which is consistent with the complaint in the question.