Not sure I fully understood, but your assumptions seem a little too pessimistic* to me.
Also, you seem to assume that the pension pot is a pile of cash in a safe that you withdraw from, i.e.
i) it does not generate income on its own
ii) you ignore that inflation reduces the pile’s purchasing power continually
I’d like to offer some … other avenues. With your goal of 72k income, you could aim e.g. for
- making a very conservative 2% income on your 2.8 million pile, i.e. close to 60k income (which you would income pay tax on, maybe about 5k total?), AHV and wealth tax still apply, and you replenish the difference to your desired (inflation adjusted) 72k by withdrawing from your nestegg, now at a rate of maybe about 15-20k p.a., i.e. forever?).
This should last beyond your most optimistic life expectancy. - make an aggressive but still realistic 4% income on your 2.8 mil pile, i.e. close to 120k income (tax yadda yadda yah), most likely leaving your nest egg intact (depending on inflation and your life time), and your additional “problem” of having to spend more than your planned 72k net.
You heirs (or the trust you’ll set up) will thank you. - … hey, I’ll one up the above in two steps:
i) make a calculated 4% or slightly more income on your nestegg and actively select your eventually well diversified portfolio to consist of both reliable dividend payers and proven dividend growth payers. Your income will even grow over time, ideally surpassing inflation but at least catching up with it.
The younger you are the more you can focus on dividend growth companies that will grow your income at 5-10% every year, the closer you are to FIRE, the more you probably want to focus on reliable dividend payers that pay a 5-10% dividend that won’t grow much (if at all) but that is reliably payed out.
ii) buy into undervalued companies that will over time (typically years) benefit from multiple expansion and bath in the sun of your nestegg expanding while you do exactly nothing.
Perhaps much more interesting to you: this latest approach would perhaps allow you to retire much earlier than planned according to your calculations.
Ok … not entirely sure whether you’re able to tell which approach I have subscribed to … 
(if you are interested, check out this discussion).
Anyway, sorry if I went into too much detail, but I suppose the path to FIRE is indeed very much detail and path dependant and IMO can be achieved with much less net worth than currently inflation adjusted 3 million at an age of 50 (unless you strongly believe index large market investing is the only path to enlightenment and are happy with a less than 2% return and withdrawing as necessarily even when the market pukes).
Thanks for putting out the question and again apologies if I misunderstood or if it has already been answered.
Good night and good luck!
* Only checked my own tables, didn’t verify in detail:
If you lived in Zurich (the city) with withdrawing/consuming 90k gross and had initially 2.8 million saved up
-
you’d perpetually pay no income taxes (well, assuming your wealth does not generate income, see my other thoughts above) as you are just withdrawing from your own capital, not generating any taxable income.
-
you’d pay AHV about 4.3k (per person, based on your wealth), decreasing over time, as your wealth decreases as you withdraw, and stopping once you reach 65 (or whatever the retirement age will be at that time).
-
you’d pay wealth tax of about 4k, decreasing over time perpetually as your wealth decreases from your withdrawals.
So 90k gross withdrawal leaves you with a little above 80k net to spend.
80k gross withdrawal would already leave you with your desired about 72k net, according to these calculations.