The alter? more like the orbs. A T1 alter by default, holds the exact same LP as a T6 does. There are runes of Enhanced and Superior Capacity that up it's capacity. The orbs need more and more LP to make as you go up, and also hold more and more. I don't really delve heavily into BM, so I don't remeber the exact numbers. There is also the Rune of the Orb that increases the orb's storage (and is needed to get to T6). It's only really the 3rd orb that is "challenging" to get. It needs you to top off the alter as it's crafting the orb, and assumes you use (self-) sacrifice runes. after that you get access to Enhanced Capacity and Dislocation runes, which make further orbs much less troublesome to get, as you can either bump up the capacity so you have enough to cover or use dislocation runes to have an adequate influx of pumped in blood.
Not the best example perhaps, but I see what you are getting at, I've always seen the flowers as being in teirs anyhow based on what was needed to craft them, Dayblooms and Nightshades needed no mana to make, so I see them as Tier 1.
Hydrogenas and Endoflames need mana petals, but no runes, and made up tier 2, but these days I'd class hydros as tier 1.5.
Next come the flowers that need an elemental rune or a rune of mana. The Rosa Arcana and the Thermalilly are the two I remeber here. (Incidently, neither of these flowers are fully automatble with just Botania and Vanilla.)
Next are flowers needing seasonal runes, such as the gourmaryliss.
Then the ones needing the deadly sin runes, I think all of these are now post-alfheim, needing Pixie dust as well.
And finally the sole flower needing a single Gaia Spirit, The Dandelifon.
I'm not sure that these tiers would fit an exponetial scale, due to the nature of how mana is consumed in Botania. There isn't much that demands a constant drain of mana, and even these in most cases are turned off when not needed. Mana is often consumed in bursts of activity, not constantly. The biggest thing I can think of that is intended to be always on, is the Alfhiem portal. Possibly Agricarnations could also be constantly draining, but even then you only need so much in the way of crops. Without withering, even a single Daybloom will eventually make enough mana to fill a mana pool completely, no matter if the mana pool holds 1 billion mana and the Daybloom only makes 1 mana a second during the day.
EDIT: Also I doubt there is ever going to be a solution that pleases everyone.