I think Exoflame flower needs a balance pass, here's why:

• Vanilla setup: fill a furnace with a hopper full of cobblestone, extract with another hopper to a chest. Using a single lava bucket as fuel, 100 cobblestones will be smelted.
• Botania setup: have a Thermalily sends its mana to 1 Exoflame next to 1 furnace filled with cobblestone.
  Using a single lava bucket next to the Thermalily, 26 cobblestones will be smelted.

While the second setup is +50% (?) faster, it's also ~4 times less efficient.
Since an Exoflame is fairly expensive to make, I would expect better efficiency without speed bonus or same efficiency with speed bonus.

This is tested with Beyond reality pack, including Botania r1.3-145

The point of the exoflame is not to be more efficient, it's to allow you to use alternate fuel methods.

When alternate is 4 times less efficient, why would anybody use it?

Well, for one, lava is a very inefficient fuel in botania, because otherwise it'd be insanely overpowered. Here's some alternate fuel sources:

• Experience Points
• Leaves
• Cake
• TNT
• Food
• The Sun
• Water

I've 64 floating hydroangeas surrounded with water powering a single exoflame. It's still not enough to sustain 2 furnaces and will periodically run out of mana.
I consider those 64 as an overkill. Sun is 10x slower so it's not an option here.
To my understanding, those 64 hydroangeas are equivalent to 1 kekimurus which requires 4 cakes per minute.
Did I miss something?

No, it's just that hydroangeas are horribly inefficient. There's also no need for excessive punctuation.