Now if running tubes, subjectively there is some argument, tubes have poor damping and hence very little bass control to speak off , a sealed enclosure might be an advantage here, TL too , due to the loading.
Actually in practice the reverse is true. Vented boxes usually need less damping of the driver for optimal response if I have my theory right- so less damping from the amplifier will be needed. So you can have plety of bass control!
No speaker known requires a damping factor of above 20:1. That can be created by any tube amplifier, given enough feedback. However you pay a price for adding feedback- while you get more damping, you also add odd-ordered harmonic distortion, which essentially is audible as brightness and harshness.
So if you want tubes to give you the best they can offer, its in your best interest to use an amplifier without feedback, and a speaker that is intended for an amplifier with a higher output impedance.
The only thing about this is that loop feedback contributes to harshness in transistor amplifiers too. Since the ear/brain system uses the 5th, 7th and 9th harmonics as a means of determining how loud a sound is, messing with these harmonics will cause the system to sound louder than it really is, plus the odd orders are perceived as harshness. So there is a powerful argument for eliminating feedback altogether, as figuring out how loud a sound is is arguably one of the more important rules of human sound perception.
IOW, the model of an amplifier with an output impedance of zero ohms may not hold water, given other real-world issues. So designing a speaker for that may not make a lot of sense either.