1: Ions are useless. Always have been, always will be.
2: Those are some terrible defence ratios. You want zero Ions, and far more fodder in general, though that's not what helps you against RIPs.
3: Best defence against RIPs, is RIPs hiding behind a fodderwall and plasmas.
Your defence proposal costs:
1.260.000.000 Metal, 745.000.000 Crystal and 156.000.000 Deuterium
50 RIPs, 400k RL 100k LL and 5k plasma costs:
1.450.000.000 Metal, 500.000.000 Crystal and 200.000.000 Deuterium
With the given techs for both attacker and defender, and an attacking fleet of 500 RIPs, this is the result:
Losses Attacker 1.360.000.000 Metal, 1.088.000.000 Crystal and 272.000.000 Deuterium
Losses Defender 362.663.000 Metal, 90.775.000 Crystal and 45.390.000 Deuterium
Attackers loses half the RIPs, Defender loses none.
(note: the above is an example for defending against RIPs. That defence will require some additional work (though still no Ions) to protect against light and/or heavy speedfleets. I does illustrate why it is important to play around with a sim, trying hundreds if not thousands of different scenarios to find the best solution for your particular situation)