It kind of comes down to this:
Kraken/Mab teams were a plague of high-end PvP because they could use a troop like Forest Troll to generate blobs like the above. They could generate multiple 4/5 matches easily and the end result was the team could easily dole out 25+ damage to your entire team in one turn THEN perform its Kraken casts, leading to more damage and filling the NEXT Kraken, and so on.
So this change was made because players wanted something to be done about Kraken/Mab. I don’t know how it affects mana counts, but I’m pretty sure the intent was to limit Tentacles to 1 per “blob”.
So now, armed with the knowledge that doing excessive damage via generators making blobs is something players don’t like, Dhrak-Zum is going to bring us Doomskull generators. I’m pretty sure doomskuls do “damage per explosion”, so they’ll circumvent these mechanics. I think that means the situation in your original post might deal 50+ damage. I’m pretty sure in short order that’s going to get toned down.