I think the biggest problem here is on the math of total trophies for the whole system.
If I lost a fight, I would loss 20+ trophies, but the defender would not gain any trophies. So for the PVP system as a whole, a total of 20+ trophies is lost.
If I win a fight, I would gain about 18 to 22 trophies. But the number of trophies lost by the defender is unknown. If the number of trophies lost by the defender is bigger than my gain, again the system as a whole would loss trophies.
If for every attack, regardless of win or loss, the system as a whole will loss trophies, then as a simple matter of math, very soon the total number of trophies for the entire pvp system will be reduced to 0, and the more attacks people used, the faster it will go to 0.
In the old system, at least at the lower levels, the total number of trophies will increase when people make a successful attack. At the higher level, the net gain becomes 0, so the system is stable.