I also have over 100M PP points made so far. Lost entire army (40mil+ off and about 7mil def) , while my past payout was of 13K proms.
So even if i have invested double than my previous reward (in terms of units/resource value) still zero payout (got left with champs yey !).
Asked them to check logs , just to make sure their system didn't bug or something (as it happens for them to have problems with the database as well). They said they checked and all looks normal. So i guess it's normal for the system to F. you up , then trow some revival discounts to lure you into reviving your army ( in my case it costs 5mil+ drachmas to revive my army that got eaten by Xerxes , darn he is hungry/greedy/plarium ).
So my only advice for everyone would be a boycott of the Persians system or use JUST light units if you really like a persian event/tournament , else they will trap/catch you one day. Even casino's have a better payout ratio than plarium's "non gambling game". I believe that the only thing that will ever make plarium to reconsider their on-purpose flawed persian system would be if players realize the truth and stop playing it together (as it's a money making tool).