sorry Fataal, but I've tested it. 3/4 zombies immediately run for the weak block. 1/4 will stick to the first block they encounter FOR a few seconds before most of those 1/4 goes for the weak block too (as it get damage).
https://imgur.com/a/p6wFTwy
21 zed, 15 goes for the weak block, 6 stick around their spot for a bit until the weak block get about 50% damage and then all but 1 goes for the weak block. as soon as one of the weak block break, the last 1 also goes there (which is fair enough) to beat on the last weak block.
Current:
https://imgur.com/a/4HveLJB
it just imo, I would make zombie ai ignore block max hp when calculating path, treating all block as the same, so it would first make a B line to you instead of work out which block is the weakest.
https://i.imgur.com/7VZ39Io.jpg
THEN each time the path is update (or about 10~20 second), if there is no changes (no block get destroy and updating the path), have the AI check 2-3 block next to them
https://i.imgur.com/lr2swcD.jpg , if it have been damage, it would switch
https://i.imgur.com/cEYXfrP.jpg, and when a new path open up, zed would use that path
https://i.imgur.com/dS9c7F5.jpg.
this way zed would slowly concentrate on a few spots
https://i.imgur.com/cEYXfrP.jpg, instead of the whole horde concentrate on a single spot as soon as a block get damage.
https://i.imgur.com/BODrN5G.jpg