TL/DR: I think that charge attack does not suit an infantry unit, so better remove the charge attack of Urumis, but let all their attacks have the blast attack of same strength, with possibly reduced radius.
Both of these units are pretty unique with their charge mechanic, but are they really similar?
The Coustillier is a medium cavalry unit (outside of its charge attack), which can charge its attack by 20/25 over 40 seconds. This promotes the unit to be used in small numbers with raiding from time to time, or in medium numbers to be used as a shock cavalry with several units crashing against enemy units dealing their charge attack and fleeing to recharge.
The Urumi Swordsman is basically the same, but with the charge attack replaced by charge area attack. So how can we use this unit? Remember that as an infantry, this unit cannot run away. So can we really use the charge mechanic that effectively?
Urumis have even more things going for them in the background. It charges its attack by 12/15 in 24/20 seconds, which is much faster (but weaker) than the Coustillier. As mentioned, they already have the area attack with the charge, with 50% effect and 0.75 tiles radius. Then you also have the unique technology to ignore armor. All these gimmicks for one unit.
So if you cannot hit and run with the unit, the charge attack basically becomes a preloaded version of regular attacks. Considering 12 attack over 24 seconds, it becomes +1 regular attack, and 15 attack over 20 seconds (Elite), it becomes +1.5 regular attack, which doesn’t sound amazing.
I wanted the Urumi Swordsmen to lose their charge area attack entirely, but their regular attacks to still have the blast attack property. The blast radius be reduced to 0.5, but the 50% effect is maintained.
The gimmick I thought was that there is no infantry with natural blast attack (we have cavalry with natural blast attack - elephants). But DoI already has the Ghulam which does the exact same thing, but limited to a particular direction.