It's easy to rule over a region that isn't really contested. The Beastmen have no real holdings of power. They can't take or create any place of any real significance. Something akin to being the ruler of Antarctica.
I wouldn't say that - men and Dwarfs need the forests for wood to use in buildings, wagons and weapons, and Forest Goblins and Wood Elves live in them. All of them of course have to get past the Beastmen in order to do that.
Beastmen are ultimately too stupid to be that much of a threat, dumber than Goblins
The fact that they regularly use Ambush tactics shows they're probably about on par with Goblins. It is more intelligent to attack someone from an angle they are not expecting than to just charge right into their face as Orcs and Ogres do. Also do Chaos Warriors have much in the way of tactical knowledge lorewise? Because knowing the way the army plays and given they're made up of simple-but-bloodthirsty Norscan barbarians, I could be mistaken for thinking they don't.
and less formidable than Orcs.
Again, I disagree. A standard Gor has a similar profile to an Orc Boy but has +1 Initiative so gets to fight first, +1 WS, +1 Movement and around 50% chance to get Hatred on any combat turn. Thus the Gor has a fair chance of killing the Orc before the Greenskin can strike back.
A poor man's Orcs and Goblins
I agree that the 7th Edition book does give that impression, but again I hold the writers to blame for that. The 6th Edition army book gave them a lot of different mechanics that veered them away from being a clone of Greenskins.
In the lore, the Vampire Counts have had a more significant impact... Manfred anyone?
What did Mannfred do of any significance other than backstab everyone during the End Times? Please enlighten me as you're such a fan.
On my part, I would hold Gorthor and Morghur as being of significant influence - Gorthor almost destroyed two Imperial provinces and damaged them so badly that they never really recovered (as well as being favoured by all four Chaos Gods), and Morghur has spent the last few Warhammer millennia poisoning Athel Loren and trolling the Wood Elves by resurrecting whenever they try to kill him.
They don't even get the blessings of their gods

. CD are blessed by Hashut. WoC are blessed by the four Chaos gods. DoC are pretty much an extension of their gods.
In 6th Edition and AoS Beastmen can take Marks, and even in 8th a lot of tournaments nowadays allow Beastmen to take marks to give the army a bit of oomph, so the general consensus is that they do receive blessings from the Chaos Gods, even if the writers of the 7th Edition book largely forgot about this (and even then Beastmen can take Gifts of Chaos, which are still blessings from the gods in the same way as Warriors' Chaos Mutations).
I would advise you look at the 6th Edition Beastman book, as it and portrayed the Beastmen as a lot more of a threat, more intelligent and far more widespread, while the 7th Edition one gave us a significant 'lore-nerf' as well as a rules nerf in significant places.
- extended reach beyond the main games (Cursed City)
Actually Tzaangors appeared in Silver Tower, so technically Beastmen do have an extended reach, but the rest of your points are sadly correct.
I'm not sure if Chaos Warriors even need to eat.
Just noticed this quote from the Warriors of Chaos book, page 31:
And perhaps that's just as well, otherwise if they did then things would get pretty messy inside their armour
Skaven were the last army to get a book under 7th. Their book was likely largely written with 8th edition already in mind.
Actually Beastmen were the last, just pipping Skaven in that regard. Skaven received theirs in December 2009, Beastmen didn't get theirs until February 2010. This can be proven by the fact that Beastmen were the first army to introduce a separate signature spell for their 7th Edition Lore,
Bestial Surge from the much-maligned Lore of the Wild, compared to Skaven who, like the other 7th Ed armies, were assigned one of the main 6 spells in the lore they were using to be their signature spell (which for Skaven depended on whether the Wizard in question is a Grey Seer, Plague Priest or Warlock Engineer).
And the fact that their book is so good does make a difference, as they can successfully function in the 8th edition sphere.
It certainly does make me wonder what GW quality control thought they were doing when they were willing to give the 7th Edition Beastman book the green light the way it was, rather than saying 'hold on, this needs work'. I do still suspect faction bias, because I just can't think of any other reason why they would allow this to happen. On one hand there were some things added that were very good, Primal Fury added some combat clout (this didn't exist in the 6th Edition one), Bray-Shamans are on the more dangerous side of the Wizard spectrum both with magic and in combat, and I can imagine Ghorgons and Jabberslythes were a lot more worth their points in 7th when Terror was so much more impactful, but sacrificing much of what made Beastmen a unique and competent army (Ambush, Raiders, Marks, Mixed Herds) was not necessary.
It didn't help either that the changes 8th made just happened to hurt Beastmen a lot (compared to Skaven who got a lot more out of it), what with Lore of Beasts becoming a MK 2 of Lore of the Wild and Fear and Terror being nerfed and thus making a lot of their units overcosted, compared to Skaven who got more excuses to make use of Strength in Numbers and saw their war machines become deadlier than ever.