Yeah, a lot of it is based on
Kellri's Encounter Reference guide, which is based on the MM from AD&D(?).
In the scope of the game, those Lairs are important because they define NPCs who have goals, motivations, and the resources to achieve them; this puts pressure on the amount of
time the PCs take to do things, making it a valuable resource. Lairs grow over time. (They can shrink, but it's unlikely without PC intervention.)
Usually the PCs will hear about a nearby Lair from rumours - orcs raiding the road, gnolls taking slaves for sacrifice, bandits robbing anyone who comes by. This allows PCs to engage with the lair a little at a time - one encounter here and there, gaining information if lucky and/or smart.
Even if the PCs don't know a lair is nearby - they're exploring new territory and either no one lives nearby or they haven't had the opportunity to ask - lairs have a pretty big environmental footprint. There are patrols in nearby hexes and the creatures from the lair wandering about - 50% of all wandering monsters are with creatures from the lair. Since they house many creatures, they will have a big environmental footprint - chopped down trees, smoke from cooking fires, even farms and gardens.
What this means is that the PCs generally won't just wander across 200 orcs all at once, and if they do it's probably because they weren't keeping a good eye out. This means that players are given a choice about how they want to approach the lair. They can handle this any way they can think of - head-on charge, sneaking in, guerilla raids, hiring some men-at-arms to harass them, diverting the flow of a river to flood them, assassinating their leaders, making deals and trade, etc.
That's how I deal with 1).
In regards to 2), I find that 4E has a pretty mild power curve. An 8th-level party facing a 1st-level hobgoblin lair all at once will probably get wiped out; they may be able to succeed by expending limited resources, but those are a lot harder to come by in my game.
These "Orc Tribe Generation" rules that I use aren't meant to provide a simulation. These lairs exist in order to put pressure on the resources of the PCs and the decisions the players make, in an attempt to give their choices meaning.