I fear this topic is derailing a bit and I don't know if the comment above was tongue-in-cheek or serious.
In any way, everybody does what he likes, but some observations / an opinion from a low-lister world-birder ;-)
1. Everybody that has some weeks of holiday and is financially able to pay for an intercontinental plane ticket, can see at least a 1000 species of birds;
--> I started with trips to India and Ethiopia that cost me around 1500 euro (including flight) for around 3 weeks, and I got a bit over 500 species on each of those. 400/trip were new. No guides (bar the odd local guide pointing out a day-roosting owl). So I got over a 1000 species for what most would consider 'cheap' trips, and this was before ebird, xeno-canto, observation, cloudbirders (I admit you had the now-defunct travellingbirders website),...
2. Still, given you can see a fair number of birds cheaply, there are very few top listers who don't go on organised tours (or bespoke tours) or use local guides, and there are some good reasons why top listers go on organised tours / have fully guided tours:
the rational mind dictates that, if you are a world birder and your priority is to see all birds in an area ('to clean up'), it's a very unwise idea to risk dipping on a number of birds and regretting it once you are back home: a self-guided trip where you risk dipping some species + a clean-up trip, is often more expensive (and for sure more time-consuming) than doing a professionally organised trip with competent guides.
In some parts of the world though, you can 'beat the market', i.e. see as many (or even more) birds self-guided, than you would in an organised tour: organised tours often have restrictions in number of travelling days (so the price doesn't get out of control), locations and ofcourse a group sometimes restricts the flexibility and reduces the chance of seeing some skulkers,...
Personally, I mostly follow the philosophy described by George Wagner: "
The idea of hiring professional birding guides to find, show and identify birds is (edit from me: in my personal opinion) contrary to the spirit of birding. As in sports, the difference is between being a participant or a spectator. However, I will accept hiring a local as a guide to show me the trails, especially so if it proves beneficial in the local community."
In this way, I can train my bird /-finder / -knowledge skills better, and I just enjoy this better than having birds shown to me by a guide. But with this philosophy, I will inevitably miss some birds on some trips. I try to convince myself that, the more I practice my self-guided trips, the better I become at finding even the most difficult birds...
So why most worldbirders are 'spectators', you can fill in any birding trip as you want: I know some people who (almost) outperform the guides in bird-finding during organised trips and are clearly participants / leaders on their own, and I know some very, very good birders who are superlazy during organised trips (as in: "it's my holiday, I pay for the guide to do the work"). Again, as long as you enjoy your birding all is fine. Sometimes I also just want to be a spectator, especially after a very hard day of guiding a group...
! I'm just pointing out the rationality behind hiring guides / joining organised tours when you're a world birder.
3. There is no correlation whatsoever between having seen a high number of species and being a talented / competent birder.
--> Ofcourse, experience helps to improve your birding, but there are many super talented birders who never venture far away from home, and there are some helpless / slow / near-sighted birders who have seen over 5000 species. There are, however, very few incompetent birders with lists (far) beyond 7000, as this does require, besides deep pockets / loads of time, more and more birding skill and determination per new bird.
With this statement, I would like to encourage anyone who finds birds at home and is hesitant to travel, because they think they will fail massively at finding birds, to just go for it. There are destinations and birds that require a guide, a stake-out, pure luck,... but there are many destinations where everybody has a good shot as seeing close to all birds that are specific to that area, without guides or with guides in specific areas (or as a back-up plan for when you feel you're failing massively
. Just thinking of Caribbean islands for the Americans, Ethiopia, (parts of) India, Gambia, for Europeans (and for those that are lucky enough to live in a country with 500+ birds that can be seen: just go and explore your country widely!).
4. While you always have certain guides stringing, I honestly think it's a rare occurrence.
--> Most birding guides I know are very competent and very honest: if they claim / report an impressive number of species, they can often back it up with pictures etc. Ofcourse, if a guide is seeing 500 species this often translates into (most of) the group seeing only 70-90% of that number...
And with that said, as a consequence, you have to have a decent level of birding to see all your target birds, even when you're on an organised tour...!
Some birds you can't just buy through signing up for an organised tour: Seeing them requires some skill / luck, with or without a guide... In that sense, some birds can be really expensive and exclusive (think about Emperor Penguin), but others can be highly democratic (think about some Antpittas that you can often see much better birding alone on the cheap, while joining a (costly) organised tour will actually lower your chances seeing such skulkers