Yes, it will be very difficult to do legs like PS2, and it needs many things for this, one of which is at least 2 major pricecuts at the right time. However PS4 will still have good legs and will pass 130M lifetime. The main reason I think in this way is because I am anticipating at least 1 major price cut, and with this there will be low end entry level PS4 at - 199$ and high end 499 or 599$ PS5. So when parents with kids go to the store, or some casual gamer go there what you think he will buy? good gaming machine with big library for 199$ or next gen super duper machine for 599$ ?
as for your points:
1. Stop with this bulls**t please. These emerging markets like brazil or india or some 3rd rate countries that don't know what gaming is are making possibly 1 or 2% of the sales ... how many of those 158M you thing PS2 did from these countries eh? I am sure that more than 95% of the sales after 2006 are from japan, usa and europe. This is just some added reason to back your theory up.
2. PS3 released 6 years after PS2, and where are 6 there are 7. It's preety much the same.
3. PS4 can get to the PS2 price because PS4 has old parts in it. I mean the blu rey drive isn't new like it was with the PS3, the jaguar chips are so underpowered and cheap .. and everything in this system is very old and cheap by now. It's matter of time for sony to do a price cut. And the reason they haven't done it until now is the good sales. They didn't expect so high sales in 2016, 2017 and 2018, so they prolong the pricecut that they may have been planned for earlier. And because of the good sales of those 3 years, Sony though that 2019 may perform close to 2018. Which it didn't mostly because (imo) of the PS5 announcement. This ruined some 2M sales for the year .. This was mistake, they could wait until 2020 for this announcement. So with this 2019 was a little bit over 14M for PS4 and now that Sony see this and their PS5 unveil event is right around the corner - next month, they will probably do the permanent pricecut on the system to 199$ for the slim and 299$ for the pro. And this with help of some good games this year can boost PS4 sales for the year to the same level of 2019, despite PS5 launch. (As I already said, the difference between both will be at least 300$ which is more than enough to not ruin PS4 sales overral) It will drove some sales away from it sure, but not many at these prices.
Only if they don't do anything to PS4 then I can agree with 10-11M sales this year for the system, but I highly doubt it.