In a transaction you pay fees so it is impossible for both inputs and outputs to be equal. The important thing is that the 5 outputs are equal.
Whirpool has a system of premixers and postmixers similar to Joinmarket's system of takers and makers. But it forces you to be both. First you are premixer in the first transaction and then you will be postmixer in the following transactions being able to mix unlimitedly without paying extra.
The problem is that this allows Sybil attackers to mix "unlimitedly" without paying extra. Wasabi solves this problem by making attackers pay for their own mining fees.
First, you have to pay a tx0 to enter to whirlpool. You are gonna mix with a lot of users getting no clue because high anon set. You can check here:
https://bitcoinmagazine.com/technical/how-bitcoin-anonymity-sets-work
In wasabi you can have 20 open wallets mixing with less than 1 million sats in each one without pay coordinator fees. A Sybil attack can be possible in Wasabi.
You blend in with far fewer potential input and output addresses from a Whirlpool coinjoin than even a minimum sized Wasabi coinjoin. Take this transaction for example: https://mempool.space/tx/0d832b9db303d4f5934c52a061af9c3c378f0243f8cbb8783d14a1d52e8cbdbb
-138/145 unique input addresses were from outputs getting remixed from 68 previous coinjoin rounds. An observer of an output in this coinjoin would have a choice of 13,615 inputs within two hops.
-150/166 outputs became inputs for 60 future coinjoin rounds. An observer of an input in this coinjoin would have a choice of 14,528 outputs within two hops.
By comparison, observers of a Whirlpool output would have a choice between 17 inputs within two hops. Observers of a Whirlpool input would have a choice between 25 outputs within 2 hops (in the best case scenario).
