I just wouldn't focus so much on design. I would focus on what I thought would satisfy me over the long haul or you will be one of those with speakers for sell every few months. This debate about time and phase coherent speakers vs steep slope will go on forever with nothing being accomplished. Everyone is in a camp and will probably stay there until they gain enough experience listening (and becoming a critical listener)to understand what they are hearing and why.
I am in the time and phase camp and got there after many different speakers and years of analysis and listening.
Technically, ALL speakers are a trade off of one sort or another. However, phase and time aligned speakers come closer to reproducing the input signal than other designs. Steep slope speakers may swoon the listener but they have scrambled the output signal compared to the signal coming in. Would you buy an amp that screws up phase and time domain (actually high global feedback amps do this)?
Time and phase speakers are not perfect and there is lots to understand but for me, they simply sound more musical. Are they right for you? Only you can answer that.
Now, with all that said, one has to decide on what it is that they are after, wether it be dynamics, transparency or whatever. It is not arrived at easily. As your experience grows (and I actually think age plays a factor here)things will change and you may appreciate other designs.
So just don't get so caught up in all the design BS. It confuses the issue and will ultimately lead you to disappointment. Find something you like and go with it.
Also, no disrespect to Joseph Audio, but do you think he would recommend something he doesn't build? It would be like a Ford dealer telling you to buy a Toyota! If someone really cares about your musical enjoyment, they would tell you to satisfy yourself. It is you that has to be happy not them!