Any form of transport that can carry helicopters and tanks and APCs and Naval infantry will be a target, so it is no different from any other vessel of its type operational around the world.
The weapon isn't the vessel, the weapon is the forces it carries, much like an aircraft carrier.
Its defence relies on the vessels it operates with because loading it up with too many weapons will detract from its original goal.
A good way of looking at it is the Mi-24 Hind.
A combination of firepower of a gunship and the transport capability of a light transport... a sort of compromise between a Huey and a Cobra.
In practise it was found that it was more efficient using a transport for the transport role unless it was being used for a very small drop of personel, so the replacement is the Mi-28 which does have a small rear cabin to carry 2 maybe 3 people in an emergency but most of the time it is an attack helo while the Hip series delivers the troops.
It is not about travelling thousands of kms and invading africa, it is about delivering a force large enough to be effective and independant and to support their operations for days if not weeks.
The Mistral class vessels will NEVER operate on their own. They will likely have support from what equates to a carrier group and will most likely include an aircraft carrier in support.
Why not just use the aircraft carriers instead?
The main defence of a Russian Aircraft carrier is its fighter aircraft.
That means fighter aircraft, plus the fuel they will use, plus all the weapons and ammo they are likely to use.
There simply isn't enough room to fit tanks and APCs and soldiers let alone the helos needed to support an amphibious operation... that is what the Mistral is for.
The Mistral is designed to carry the armour, the aircraft, the troops, and all the stores and fuel and food needed for the operation, plus it has something like a 100 bed hospital with state of the art medical facilities so as wounded are brought back to the Mistral they can get high quality care as soon as possible a helo flight away.
For disaster relief you can swap the soldiers for aide workers and the armour for 4WDs and trucks to distribute food and supplies and of course the helos will be invaluable for such an operation and the hospital beds will no doubt be used too.
I think they will likely fit KASHTAN-M to it... front and back too I suspect, which should have minimal effect on its operational performance but improve its self defence capability without completely changing the vessel.