2. Evolutionary theory for viruses says that each new virus mutates to become more spreadable but less potent in terms of damage to the host. (The transmissibilty-virulence trade-off.)

That isn't the case. Its *often* the case but not always. As a lot of mutation is essentially randomised they can sometimes pick up a trait that can make it more deadly to all or a certain group of people that wont always be selected out if it doesnt affect replication that much.
Vaccine induced polio is a useful modern example of something evolving (multiple times) towards a more lethal/problematic variant. There are some other examples.
3. If this doesn't happen, we would have been wiped out by a virus already.

Not really, immunity is an evolutionary arms race. Viruses evolve and so can hosts. Quite a lot of viruses (and other pathogens) wiping out or almost wiping out hosts. Tazmanian devils, fungal issues with frogs etc.
4. This seems to have happened empirically with every virus we have ever experienced. AIDS is a good example.

Except as above, it hasnt. Its common but not always the case.

Other factors, sometimes a virus can evolve so its less deadly to one group of people but that change makes it more deadly to another group, demographic or population.

There can also be a stage where sometime evolves temporarily to a worse variant before going back to normal (but this takes time, sometimes years). Examples Spanish Flu, some Ebola type viruses.

There's also the risk of recombination/antigenic shift and so on that can suddenly create something far worse with no warning. The more you have circulating, the chances of this increase.

I have been viewing the situation much like you have and come to the same conclusions. With regard to the 'bio-weapon' option I have been thinking about what might disprove that possibility and have come up with a couple of general observations. First if there were genuinely a bio-weapon why are officials constantly being caught out flouting the rules? I have seen a number of videos where people 'in charge' and not knowing that they are being filmed have not been wearing masks or have whipped them off quickly when they think they are 'off camera'.

There was a very revealing video just a couple of weeks ago (in the US, I think) where an official standing behind a curtain was given a mask to put on immediately before he went out on stage and he then whipped it off five seconds later as he appeared in view, to give the impression he had been wearing it for ages. If they really thought there was a bio-weapon I am sure they would comply fully without fail...I know I would. Similarly Boris Johnson and Matt Hancock seem to think it's all a bit of a joke in between fake emotion - remember the jovial elbow bumps that they indulged in at the outset?

My suspicion is a combination of your (1) and (2). The advisers may well be influenced by their 'sponsors' etc but the politicians really are thick incompetent individuals who swallow everything their scientific advisers tell them without question. Or there is bribery or blackmail running rife influencing the course of events.

I wouldn't completely discount your option (4). Suspicions must be aroused by the rush of global governments to preach the WEF 'Build back better' mantra when talking about using the opportunity of the 'pandemic' to create an improved 'new normal'.

It is all something of a mystery.

If the powers that be truly fear that this will not behave like every other virus ever, then why?

1. They are incompetent and have not listened to people who have studied viral evolution 101, such as Mike Yeadon?
2. They have a vested interest in vaccine profits?
OR
3. They know that this is a bio-weapon but aren't letting on except indirectly by not expecting it to act like every other virus.

My money is on (2) ... but is this sound logic? Have I missed anything?

The whole problem is due to ignorance. Full stop.

Even if there are vested interests somewhere, or even if it is a bio-weapon, not all the perpetuators could possibly be in on the deal. It is their ignorant actions that have implemented the problem. They are the sine qua non.

If those that we elected to power had proper scrutiny of the science and the evidence, plus a modicum of capacity to reason, it could all stop. As it is, they are hampered by an over-riding concern for their own image and attempt to cover their errors.

Bioweapon is unlikely (its a pretty terrible one if so).

What isnt impossible is accidental lab escape. Possibly following gain of function studies.
We know (i) Wuhan has failed biosecurity audits and (ii) several people connected to it have a history of gain of function studies.

Then there are the strange, undocumented edits to sequences on GenBank, renaming, things from years ago appearing as this year and so on.

There's also the fact that normally during a species jump a virus mutates rapidly initially as it adapts. SARs2 didnt implying its either been around longer than we thought OR or had already adapted to human cells.

It maybe natural or maybe lab escape. There is murky data for both.
Bioweapon no, pointless and poor. Accident is far more plausible.