The breaker would be specified according to the supply cable size, I wouldn't say it's incorrect for the application and Merlin Gerin are pretty reliable kit. Usually the fan motors and compressor motors would be protected within the machine using thermal overlaods/manual motor starters/DOL starter with thermal. Maybe the soft starters also incorperate protection for overlaod.

Do the compressors and fans and pumps all have individual MCB's in the control panel? Are any of these tripping as well or just the main supply MCCB? Are any of the motors configured star delta?

I would start by IR testing all components @ 1000v with the possible exception of the compressors at 500v if they're hermetic. If they're semi or open compressors then whack them with 1000v as well and see if they flinch

How do you know it's tripping @ 70A sometimes? Were you monitoring all 3 phases? Was you ammeter measuring true RMS?