It's rare. Mainly it gives only 1
Note that rare. The chance of an anchor grass changing to grassland is the same as the change of a rock changing to anchor grass.
And by the time we get 5 terraformed tiles / city we already won!
Hopefully. But larger cities and economies will help to power us there.
The second mistake of this calculation is that 13 extra water will not give you 6 extra specialist, only 1 (or 2) because the other 5 new citizen will actually work those tiles. (Imagine, when the 1st new water source is available you remove 1 specialist to work that tile, to get the bonus, which means you lose a bunch of GPP while growing again!)
The citizen working the tile still provides a large income from doing so: 1w2h4c for a cottaged tile on anchor grass, and an extra hammer if we convert to planned economy.
And we are already working a lot of those tiles anyway, for cottages and wells and dew collectors. When those tiles change, its a pure income increase.
Its free extra income, no matter which way you look at it.
And the GPP aren't really the point, beyond the first few great people; the point is the income from tile yield or specialists.
And no, you have to invest workers turn, to improve those tiles to cottages, but in this game it's already done.
And in almost every game. Cottages are cheap.
As for game i think its time to focus on numberless military
But that's the beauty; there is no contradiction between getting a larger economy through terraforming while also building just military. It doesn't cost us anything.
In my solo games I wasn't very impressed by Firefly bombers, they are ineffective bombing down defenses, better to use them striking units
Yes, striking units is what they are best at. And they are very good at that, like bombers in vanilla.
since Mortar tech and ML tech
Yeah, this is an issue, mortars don't get much play. I'm not sure what the best solution is. Bring mortar earlier? Change pre-requisities for the the techs?