Again, it varies with what criteria one wants to focus on.I've played most of the official adventures put out by WOTC. And most encounters in those adventures feature enemies who primarily focus on melee attacks. And most feature dungeon like environments with relatively small rooms as a primary focus as well. So, I can only speak from experience, but given my experience is with the official adventures, I don't think it lacks representation.
In response to my observation about an owl within 30' of thecdnrmy bring vulnerable, you referenced both melee foes and enemies focused in melee.
I then specifically called out non-ranged adversaries. Basically, you seem to want to refute the vulnerability of the familiar at the ranges it needs to be to do its flyby help with "melee foes" at one point and use "melee focused" as your reference for assessment.
But my goal posts remain the same- what can attack and kill the familiar. See, that way, I font hsve to fuss with vague definitions of what "focused" means.
I wont claim to have run through all of the WotC adventures and done an exhaustive analysis, but I have read thru most of them, I borrow a lot for my homebrew.
Taking PotA as a case in point, looking thtubthrir monsters sction ehich fntsils mske of the key foes used thought the main plot, including their minions, it's like 5 to 1 ration between NPCs thst csn strike st a owl that is at 30' with a means of killing itand those who cannot. The ones that cannot are essentially their monks and heavy knights mostly.
So, of scenarios using those creatures specifically called out in the products core list - dedicated chapter - it would only be encounters that used only about 20% of those and only when it was just them.
Having also drawn more than a bit from that product, I can easily say that I would be shocked if "most " of their combat encounters of any significant challenge at all were actually gonna fit that bill. (So, not just counting fntries here, but also looking st how they were used,)
But, hey, if when you run them, most of the encounters festure only enemies who csnnot threaten the flyby familiars without ready actions - that can definitely help frame your viewpoints on familiars.