Can you tell me where you get your maths? In my recent history, the lowest LP reward I got for a victory was 80, up to 99, excluding the FWOTD bonus; the lowest I got for a loss was 54, up to 79. Median LP gained over 3 days (19 games, with 1 null remake) was 104 per game. (Without that free 300/19, median would be 79). All of that without any boost.
Game lengths varied between 21 minutes and 45, with the median being 32 minutes. (Values taken only from the minute slot, excluding seconds, for convenience.)
So your "outlandish example figures" are almost exactly correct, in my experience, minus where you said "win all games".
You also failed to actually factor in your bonus 2100 LP. So after three of these boosts, you get a fourth champion for free.
And as long as we are talking about no-lifers, which you continually brought up in response to someone asking about "people who play 'a shit-ton' and 'win a lot'." -
I'll throw my name in there. When I play on League, most days I go for 12+ hours, which should be long enough to discount the "queue time" rebuttal.
It sounds super nit-picky, because it is, but saying "It's NEVER worth it" is incorrect.