Indeed. You can electronically bass-boost a small speaker to hell and back, but that's not going to change its excursion-related limits in terms of level handling down there. This is known as Hoffmann's Iron Law - small, deep, loud, pick any two. This is why e.g. the D3V has various bass shelf options to choose from, and why the iLoud Micros' DSP will throttle back the bass output at higher levels (which apparently can lead to some odd artifacts during music playback at elevated volumes but seems to work quite well for gaming). Speakers in this size class would not be viable without a bunch of help from the electronics department, alongside ultra nearfield listening around 0.5 m.
Physics work against smaller drivers on several fronts: Radiation area is the obvious one (Sd for a 5" driver is about twice as large as for a 3.5", and up to 3 times as large for an 8" vs. a 5"), but maximum excursion tends to shrink as well, which is two strikes against the bass department. Not to mention the lower efficiency so you have to stuff in more power for the same output, which is not going to help distortion related to electrical nonlinearity any (plus, smaller voice coils tend to have lower power dissipation).
You can address excursion, linearity over excursion, electrical nonlinearity and power dissipation with solid engineering, but that's going to cost you dearly - if Purifi were to release a 3" driver, I reckon the pair would cost about as much as the complete D3V set, making a complete speaker insanely expensive. Something like the iLoud Micro Monitor Pros is likely to be about the maximum that the market for tiny speakers that pack a punch will support. Those are actually more expensive than a pair of 8" ADAM T8V, and take a guess as to which one will go louder (by no small margin at that). Apples and oranges, I know, but just to illustrate the point: When you're picking a fight with physics, physics have a habit of giving you a hard time.
That being said, there is quite a bit of variation within each size class left, so the fight is not entirely hopeless. A good 5" class monitor like the Neumann KH120 II has drivers that come very close to a good budget 8" like the ADAM T8V (and will surpass a mediocre one), and those drivers actually are maybe 6 dB short of Purifi levels still. Kali and JBL budget 5" to 8" drivers may be some of the worst for electrical nonlinearity (but tend to provide decent enough excursion), it's a good thing Kali released some 3-ways.