Let's actually talk about the size before we get our datamine.

Here's the list of past generations in how many were shown officially before launch, Gen 1-2 excluded for obvious reasons.

Gen 3: 37 of 135
Gen 4: 30 of 107
Gen 5: 52 of 156
Gen 6: 42 of 72 (69 at launch).

The worst of this, of course, is Gen 6 revealing about two thirds of itself at launch.

Right now, we have 54 officially shown off.
We know the starters have final evos and Pikipek evolves twice from official sources, putting us at 59.
Then, let's talk what's "confirmed" through leaks.
Toucan is its own thing, Salandit evolves Marshadow is next year's mythical and not the third of the legendary trio, and some presumed-legendary hinted by what was either a solar flare or a volcanic spew . (Riddler, and some backed up by others). Two-stage snowman line, two stage darwin cat, a dolphin (Chinese Leaks). Somehow a common prevo of Solgaleo and Lunaala (Team Skull Trailer Leak).
That, at minimum, is 11 more. Putting us at bare minimum 70.
We have a number of pokemon very likely for evolution like Pyukumuku, Wimpod, Minior, and Komala. At least 74.
We know that there has to be 3 other guardians we don't really know anything about, 77+.
Assuming that "questionable to evolve/evolve from something" Pokemon like Ribombee, Mimikyu, and Crabrawler, Oranguru, and Passimian are all one-stage things.
I can't trust that, barring legendaries, we have only about 5 new "Lines" of pokemon to be shown off to squeeze into the feared "80" new mon bar.

I feel like there's been this fear that the work to produce a game at this scale for graphics and shaking up the formula would have cost in design capabilit and that oversets the tradition that the odd numbered generations have brought the most to the table.
But, this is the 20th anniversary game they've been working on since around X & Y's release.
I feel like 90-110 new Pokemon accompanied with 20-30 Alolan forms is our additions.