Fleahopper's damage reduction due to decrease in AP cost is approximately correct (26 - 9 = 17 for -1 AP cost). However the crit buff reduction is a huge nerf (7% to 3%).
The Flealine Army's damage buff is quite difficult to achieve max stack. 5% per flea hit up to 80%. In other words, 16 hits. If you spam Flealove (not the glyph) and fleahopper, it will take about a bit more than 3 turns to get. With the buff in DPA (damage per AP) of Rough Tongue, it's very encouraging to not use a Flea spell. Yet again, after all the buff, the damage output is still nothing outstanding.