Does size really matter...

In 1951 Leo Fender's musical instrument company released an electric bass guitar. He wasn't the first, as electric bass guitars and bass amplifiers were around at least 12 years before. What Fender did was mass market guitars that were manufactured by using ready-made components that could be assembled. This technique was different and Fender held a US Patent for the design. Prior to that, they were individually hand made... a slower more expensive process.

To go along with his bass guitars, Fender released a bass amplifier in 1952 called the Bassman. It wasn't the first, as other companies like Ampeg and Audiovox were already on the market with bass amplifiers. Again, it was marketing skills where the Fender amplifiers were good sales.
The first generation Bassman had one model had a single 15" speaker in an open back cabinet. In 1954 Fender redesigned the Bassman model with four 10" speakers, also with an open back cabinet. Problems with an open back cabinet is half the sound gets lost behind the speaker.

The 1960's brought more changes for the Bassman to be a closed back cabinet with two 12" speakers, followed by a Showman model with two 15" speakers in a closed back cabinet. The Showman was impressive, but wasted lots of space with the size and difficult in transporting to the gigs. That design was called infinite baffle.
By that time, there were lots of bass amplifiers available from different companies usually using 15" speakers in smaller enclosures. Ampeg who started before Fender had a model using an 18" speaker in a compact cabinet called Portaflex that could easily be transported. Good for recording studios, night clubs and small venues, most musicians needed something larger to project the sound to the audience.
Nearing the late 60's Acoustic had a model 360 with one 18" speaker in a large cabinet. The design was called a 'folded horn' and more efficient than anything before it.

Marshall in England was producing cabinets with four 12" speakers that for some has been a standard. Available with speakers suitable for guitar and speakers suitable for bass guitar. If you've been to a rock concert or seen videos, stacks of Marshall speaker cabinets show the audience you are rock royalty.

Everything has limits and speakers in the 50's and 60's could only handle power of 20 or 30 watts. Too high of power would burn out the voice coils. The more expensive ones were less than 50 watts, giving greater output of sound.

So the theory was more speakers were needed for higher wattage.
Speaker designs improved and manufacturers were making models capable of handling 300 watts each.
That started a different set of problems. While the speaker could handle more watts... the paper cones were failing at the flex points around the edges. More research came up with rubber edge allowing for more movement.
They were loud and didn't break apart.

Size wise the industry had 18" woofers for deep bass, 15" for bass and guitar, 12" for bass and guitar, 10" for bass and guitar.

Years ago, Ampeg created a new standard that many rock bassists continue to use. Eight 10" speakers in one cabinet. The theory is, it handles 1,600 watts of power and the 8 speakers are coupled to move more air than any other design.

In 55 years of playing bass, I've tried lots of different combinations... 10's, 12's, 15's, 18's and my favorite speaker size was probably 15" because it develops a nice bass sound even at low volume. I've been shopping for a practice amp loud enough for a small venue and I'm finding most of the 200-400 watt amplifiers available have a pair of 10" speakers.
That combination gets the most wattage, most sound in the smallest package.

So, maybe size doesn't matter.