Yes, shieldwall gives a huge defence bonus & totally destroys the intended balance unless you drop off the other stats in compensation & that requires a seperate EDU.
Also, EB have already set the formation spacing as they intend it to be, shieldwall puts the units even closer together (to the point the RTRPE hoplites are constantly 'treading water' to keep in position against the game engine algorythm to force too close units to spread out.

I'm happy with hoplites as they are in EB without shieldwall.