Not an expert but the biggest difference is likely to be more up to date fire control and battle management systems in the Challenger 2, as well as a better sensor / imaging package.

This will mean they can more effectively find and target enemies in the Challenger 2, as well as having better integration with other units.

On the other hand, the Challenger 2 has a rifled barrel on its main gun because of the ammunition British forces like to use, which makes it a bit of an oddity and it may be easier to find compatible ammo for the T72's smoothbore gun.

But the UK also has a much bigger military budget so this is indeed an impressive contribution from Morocco.

Most countries running old Soviet era tanks donated their old stockpiles, as Ukraine already knew exactly how to use them.

The British army use the more modern Challenger attack, their own domestically made tank. Most European countries use the German made leopard, which is a similar specification/era, but has been produced in vastly greater numbers is much more widely adopted, allong with parts and expertise.

The thing about British tanks is that you don't really need many of them to defend an island.

It's definitely a huge contribution, but those 12 challenger tanks are as well. As you noted, the difference is in the tech. T-72s, even "modernized" ones, are still cheap tanks from the 70s.

Modern MBTs like Challengers, Leos, and Abrahms would still eat T-72s alive on the battlefield in a tank on tank fight.

As a quick example, a Challenger 1 in the gulf war has held the record for the longest range confirmed tank kill, destroying an Iraqi MBT (assumed to be the T-72) from over 4500 meters away.

On the contrary, a T-72 needs to be within 1000 meters of an Abrahms to even penetrate it's armor. Assuming somewhat similar performance for a Challenger, you can see why the 12 Challengers can be so effective.

Btw, allegedly a Ukrainian tanker has now beaten that long range tank kill record, but I'm not sure if that's confirmed or just one of those military stories that gets spread around for morale.