Firstly this is a question perhaps better aimed at the designer of this (or any) particular arrangement as they'll be able to talk you through their design.

(Perhaps arguably) not all MCCBs incorporate protection; for larger currents a switch disconnector is in practice an MCCB that's not been supplied with a trip unit. Random Schneider example.

MCCBs with TMD (thermo-magnetic) protection may, or may not, be adjustable. If they are adjustable, you might be limited in settings (commonly you might only be able to adjust the thermal element).

MCCBs with electronic protection relays will be adjustable, to allow finer control that the designer may need; for example to achieve adequate discrimination. They may also have additional protection functions, which may be integral to the "standard relay" (for example, an I2R protection mode may be provided to protect against "ratcheting" from repeated reclosure onto faults) or bolt-on extensions (for example a Restricted Earth Fault feature, or intertripping / blocking for zone protection). However, the downside is that they do cost more and of course need to be commissioned correctly.

Whether overcurrent protection alone is sufficient for earth faults, and hence whether a specific earth fault function (and at what level of sensitivity) will depend on the nature of the supply, circuit and load, and is for the designer to determine.

Basically it's a balance between features required by the designer versus cost and complexity: When all you need is an oversized MCB for the final circuit to a machine, it's hard to justify paying for - and maintaining - the whizziest gadget with all mod cons that'll never be used (or if they are, tangibly add to the safety of the circuit being protected). I suggest you have a look at an MCCB brochure and then some distributor costs for the various options.

Hope that helps.