ORIGINAL: Pippin
I have seen France with control of the UK. The amount of gold, manpower, and other penalties she can now inflict on everyone else, (e.g. knocking out all trades, etc) is huge. Perhaps you are right in that it does not mean France wins 100%. IIRC, as soon as UK falls into French hands everyone just wants to quit the game at that point anyhow.
If Britain is smart and gives a surrender early, then she will still get cracked on the head pretty hard, but perhaps she will live if Spain for example decides to remove her alliance from France.
Once France gets her corps into UK soil, she will make sure through every means possible as soon as any enforced peace time is up, her corps will have a guaranteed method of re-landing for another go.
Even a smart Brit who keeps surrendering early each time to save what it can, will just end up in a downward spiral of getting weaker and farther behind. Coming to a point where there is nothing left of her and it will end up in France's hands mostly.
Trying to rebuild the navy? Don't bother! You know she is going to lose 2 fleets on every surrender... lose any minors... and all trade will be banned. Not to mention worse problems when France isn't the only one getting repeated surrenders out of her.
How can France make sure to land safely in GB every 18 months?
The only way to do this would be to have a comfortable naval superiority over GB. Depending on the continental situation, this can be problematic.
Additionally, antagonizing GB over and over will offset most of the gains through reparations etc. Normal french trade with GB is often in excess of 20$. Should GB deny trade with France during the mandatory peace duration, that's 120$ lost right there.
Let's take the worst case scenario regarding reparations in this case: that's 34$ *2 = 68$, plus half the trade for 4 economic phases = 60$ from colonial trade, and assuming GB does not trade with France, about 80$ from trade in the best circumstances. So France in the best of conditions will end up roughly 80$ ahead every 18 months - Hardly a huge amount and certainly not enough to offset the cost of wars against GB.
I fail to see how France could mathematically ensure beating GB every 18 months, and also fail to see how achieving that would get her so much ahead.
Even using the mandatory war option, the main threat to France security does not come from GB, but from the Prussia-Austria alliance. the removal of GB one way or another would be a major boon to France, but my no means a guarantee of victory. Also consider that countries like Russia or even Turkey can replace GB in an anti-french coalition with far greater effectiveness than GB could manage in most circumstances.
In the initial 1805 situation it should be a relief to both GB and France to not be at war. France because war with the germanies is unavoidable in the short term and they represent the most important threat, and Britain because her interests tend to clash with Russia and Spain more often than not, and 64 less ships to worry about is a big difference.