Typically with different cinematic and music formats only a certain amount of information/sound is sent to the rear channels. In having towers as the rears your main disadvantage is that they are very under-utilized.
Unless your towers are designed to have the LFE subwoofer bass built-in. Thus, each tower also serves as another subwoofer. In rectangular symmetric rooms, 2 of the best subwoofer placements are 1) the 4 corners and 2) the 1/4W front & rear wall placement. So 4 towers = 4 identical subwoofers @ the 1/4W placement = smooth bass + SPL increase. Here, the towers in the rears are not underutilized IMO.
Case in point is the RBH SX-8300 towers. Each tower has about the equivalent bass of one RBH SX-1010 subwoofer. Each tower is fed with LFE from the processor/AVR.
Supposedly, ATMOS/UHD/AURO may also have beefier surround effects even in 5.1 mode. So the surround speakers may one day be significantly utilized more than in the past.
But as others have said, there are many was of doing things. Bookshelf speakers are fine and so are big towers if that is your fancy.