I always asked myself which is the aim of having unit types with different (higher) base HitPoints and FirePower.
I mean, in practical terms these features could be replaced by accordingly increasing Attack or Defense ratios for each unit type. E.G. a Musketeers (20hp/3Att/3Def) would be the same if 10HP/6Att/6Def.
I may be wrong, but about FirePower, the difference between a unit with ATT=3 and FP=2 and a unit with ATT=6 and FP=1 (respectively double and half of the previous one) is almost irrelevant, and I bet that stats would be nearly identical.
About HP, I would say almost the same: a unit with 20hp is almost the same as a unit with 10hp but with both attack and defense ratio exactly the DOUBLE than the former one. That's the case of Musketeers (20hp, 3att) and Catapults (10hp, 6att). Their attacking odds are almost the same. The only relevant difference (a part from the Defense values) would be that after the same winning attack, and losing 50% of original hps, the unit with the highest base hp (Musks) would have to wait more turns to regain 100% health, and thus it would be a bit, and just a bit, a worse choice than its counterpart with double the attack and the half the HPs (Catapult).
I bet that this was not the original porpouse of introducing different HP values.*
We all know which was that purpouse. It was that many Civ1 players complained that when they had a superiour army there still was a d****d AI Militia resisting against our brand new Battleship.
To help those poor frustrated players, Civ2 introduced HPs, which RADICALLY helps the best units and makes impossible to beat a far superior unit (at the cost of introducing DAMAGE for the winning unit, a cost which I rate far inferior than the advantages this unit gains).
I have been always a fan of Civ1 and my slogan has always been "The Militia can defeat the Battleship" (see http://forums.civfanatics.com/showthread.php?t=377576). I do believe that the introduction of HPs adds interesting variables to the game but also FAR ENOUGH help for superior units.
Anyway, it looks like frustrated players were not satisfied and they wanted that superior units were almost INVINCIBLE, better without "almost". That's the reason Musketeers DOUBLED their power (thanks to the 20hp) and many later units multiplied x3, x4, x6 their power thanks to the multiplier given by high HPs and FPs.
In general I don't like steep power curves of units, cause I think there should be ALWAYS hope for the losing ones (as well as ALWAYS thrill for the winning ones) but in any case, I think Freeciv's power curves are by far exaggerated.
What can be done?
Simple. Let's abolish different base HPs and FPs. We'll gain 2 advantages:
1. More linear and less steep power curve of the units ("The Warriors can defeat the Helicopter")
2. We get rid of 2 variables which are just redundant and we save mental computing.
I can understand that (1.) could be too radical for many players (some units may have a "real" attack power 2, 3, 4 or even 6 times smaller than before), so I would agree in making up the Defense/attack values (e.g. Musks could be 4/4 or 5/5, still powerful against medieval units but not almost INVINCIBLE as before (a "real" 6/6).
Another making up for helping the superior scientists could be thinked of, but in any case I think the advantage technology gives in LT/GT games is immense and could be rebalanced.
* I didn't check if with some special rule (e.g. with special units and special defensive facilities) our "HPs/FPs vs. Attack/Defense" difference MAY become relevant and anyway THIS would still not be the purpouse of HPs and FPs.