Roman cavalry casualties vs phalanx

My cav units take about 30% casualties in charges against Seleucid phalanxes even if I take care to charge to the rear and pin them with an infantry in front. I get annoyed when cav units lose a few horses on contact. The animation shows horses get squashed in the charge or thrown head over heels on contact but pikemen don't seem to die in proportionate numbers for the same reason.

Should I stop re-charging and leave the cav in-place and duke it out? I read the butt spike reason but I don't think its true since charges to the flanks are less successful because the horses creep to the front and really get skewered.

Another observation is that Seleucid and Macedon phalanxes are cheap for a 120 man unit. For 650-750 denari most other factions get a good 80 man unit. It takes a while longer to hack and hew through 120 vs 80.

Yes, but the levy pikemen come with poor morale, so if you manage to rout one or two, preferably at the flanks, their whole line will collapse and rout, even without making contact with your troops.
As for the cavalry, it may be a version thing, I´m playing with 1.2 and I never noticed such a thing. And I do use Equites to rear-attack phalanxes. To let them slug it out is taking a fifty-fifty chance: If the phalanx keeps fighting the infantry, they´ll be fine, mostly. They´ll still loose some men, because the phalanx men aren´t that stupid not to realise that there´s someone poking spears into their backs. If they turn, however, they´ll cut a lot of your horsemen down in the swipe, but they´ll get slaughtered by the infantry in their back. They´ll be dead one way or the other, it´s just the number of men you´ll loose that´s a bit unpredictable.
Plus, the melee skills of the roman cavalry aren´t awe-inspiring, to get the best out of them you should rather use what charge bonus they get. At least that´s my opinion.

Levy pikeman? Unless versions really have different unit sizes, Seleucid and Macedonian infantry above crappy peasants and militia are 60 men units(120 on large) which is 1/3 bigger than most other factions.

I didn´t claim anything else. There´s militia phalanxes (the most basic ones) which have normal pikes and levy pikemen (one step above) who have the extra long ones.
Or do you talk about the "one or two"? I was referring to units, not men, of course. You can´t rout individual men, now can you?