There are three points to make here
ONE - effectiveness is no guage of whether a unit should be represented. Plenty of crap ideas floating around and costing lives in WW2.
TWO - There are a number of units/concepts represented in game that didnt work/never got finished/never got a chance to fight due to time/fantasy.
Obviously these are there for a fun factor or a whatif?, you need to compare something like the Maus v other stuff (nuke ships, helicopters etc etc) and replace with another fun unit if you can justify it.
SHA certainly qualifies as a whatif? And fun is just personal but I give it a thumbs up for fun.
If the disadvantages are accurately depicted, it would be more useless than militia, and thus won't ever be built, forever occupying a brigade slot for no good reason.
I say ax 'em.
THREE - Arguing effectiveness is very difficult, what information do we have? And what situation are we in? And what value is cost effectiveness?
Most arguments about effectiveness seem silly "oh it will break the roads, or cant move move then 2 mph etc etc" Would it actually? Do you know or are you using cartoon logic - big heavy things must break stuff and be slow!!!!
How silly a battleship, must be barely able to move, arty has contest to see who can it it the most, no dock could ever support it.
I dare say there are well backed arguments for an effectively used SHA unit, just as there were for battleships.
Even when air power showed the shortcoming of a battleships, they were still used, and still had potential. Not "more useless then militia"
Now if you want to spend the money for the minimal return is up to you, but make real arguments.