I am not sure what was the real intention of this nerf
I can tell you the exact reason
They nerfed the Frog Prince in order to eliminate an "exploit", which, under some circumstances, made it possible to reduce your "normal" avg. losses by 300-400%. I'll explain what I mean by "under some circumstances".
The huge attack range (10) of the Frog Prince, combined with the fire phoenix attack bonus (+50%), combined with T.o.t.Toads attack bonus (37-40%) resulted in a possibility to eliminate enemy light melee and light ranged units
with one shot (the attack bonus is the key here). The result was, that light enemy units died instantly and the Frog Prince had all the time in the world to eliminate all the other enemy units (even heavy melee) with nearly zero losses. You needed T.o.t.Toads at level 27 or higher to be able to achieve that effect.
There was a huuuuge difference between a fight with T.o.t. Toads at level 25-26 (or lower) and one with T.o.t.Toads at level 27 or higher. With level 25 you had a normal fight with normal (though very low) losses, but with level 27 the Frog Prince became almost immortal.
The reason was:
1. With level 25 the Frog Prince weakened the enemy units, but wasn't able to kill them with one shot. It needed one more shot in order to eliminate them. In other words, the Frog Prince "lost" his second shot and in the meantime, other enemy units could come closer and had a chance to land a hit in a third round. That's a normal fighting mechanics.
2. With T.o.t.Toads at level 27 or higher the Frog Prince could kill some enemies with his
first shot from across the map, so the Frog Prince had one additional round to eliminate all the other units (heavy ranged and heavy melee) before they came close enough to cause some damage. One additional round means the difference between low/normal losses and
zero losses.
That resulted in a sick situation, certainly not intended by the developers. The Frog Prince became almost an universal unit, you could use it in many tournaments in round 1 and 2 with zero losses. In gems tournament (rounds 1-4) the Frog Prince achieved better results than the Blossom Princess with 8x Mage Multiplier !!! I consider that an exploit, since it was certainly not intended by the devs. It changed the whole fighting balance.
Under these circumstances (Fire Phoenix + T.o.t.Toads at lvl 27 or higher) the Frog Prince became much too powerful, it became an universal unit and not a specialized one, as intended. Shortly speaking, these "circumstances" (only few percent attack bonus too much) made that unit totally overpowered.
Some people might think that I'm exaggerating, but I'll give you an example.
Elixir tournament:
City 1:
1. Frog Prince + Fire Phoenix (+50% attack) + Temple of the Toads (
+20% attack bonus),
7x Unleashed Unit Upgrade
87 provinces, 23490 points
Losses:
1500 units
City 2:
2. Frog Prince + Fire Phoenix (+50% attack) + Temple of the Toads (
+37% attack bonus),
2x Unleashed Unit Upgrade
84 provinces, 22680 points
Losses:
500 units (avg. losses in the whole tournament: 0.14 units/fight).
As you can see the attack bonus difference of just 17% caused such a huge difference in losses (1500 compared to 500) although I only had 2x Unleashed UU. My later tests showed, that even the difference of just 4% would have a similar effect.
Some screenshots, showing
most difficult fights in the 3rd and 4th round, that's sick:
I reported that to our CM back then, using almost the same description and the same screenshots and he forwarded it to IG for further investigation. Why ? I don't like such "exploits", I was also one of those, who protested against too many time boosters and against the possibility of gaining more than one bear. If someone wants to blame me, please don't
Thinking that the nerf is a result of a single player's report would be naive and of course it's not the case. Moreover, IG's reaction shows me that many other players must have noticed and reported this problem as well. And yes, I consider it a problem since it affects the game balance too strongly. It gives a small group of players a huge advantage over the others.
I deeply believe the nerf was necessary. It will be easy to compensate it for an average player (5 levels of the T.o.t.Toads will be enough), but it will prevent that small group of players from using the Frog as an universal, almost immortal unit. I estimated the necessary reduction of attack bonus to be -10%, but apparently -8-9% will be enough, they must have calculated it better than I have
Conclusion:
IMHO the nerf was necessary, so that the Frog Prince even with T.o.t.Toads at maximal level won't be able to one-hit-kill the enemies from across the map. That was exactly the problem, which destroyed the normal fighting mechanics. The Frog Prince will remain a very strong, powerful and useful unit, but it won't be possible to "exploit" it any longer in a way I described above.