Difference in opinions. Everyone has a different experience. Some people have used both [bookshelf + subs] and [towers + subs] and they truly believe 100% that they get the SAME quality in every aspect from both.
I think the biggest difference isn't "soundstage" or "imaging". I think it's the difference in speaker Sensitivity and Dynamic Range.
"There is no replacement for displacement" and "you can't defy the laws of physics" are popular sayings.
Bigger drivers plus bigger cabinets = more displacement = more dynamics = less distortion at high volume.
But what is your volume? Is it high enough to to worry about Dynamics? Do you wonder if your speakers are "distorting" at certain volume?
And BTW, I use "bookshelf" speakers that are about 31" tall, weigh about 100 LBS each, and have more dynamics than most towers.
Here is a picture of my "bookshelf" speakers sitting atop subwoofers.
Gene also has these bookshelf speakers, except they are sandwiched between 2 subs.