I don't disagree with your argument, but your data is incorrect. Looking at heavy cavalry/tank alone, the numbers fail to account the increase unit space tanks take up (10) vs. the standard horses (6). Also, wiki is no longer an ideal source for data mining as some articles have not been updated following recent revisions (i.e. nerfs). Furthermore, some wiki numbers seem to factor in a boost given by research and wonders while others do not (grossly inaccurate). For example, the base DPS for my French tank is 288, less than the 300 wiki gives for your standard tank. This would be impossible, as the French tank has a 15% increase in DPS over the regular tank. I have kept some numbers, which may present a more accurate picture. I believe the base stats for lancers and cuirassiers are accurate, however, the revision for [or base stats for] a standard tank should be: 11,000 hp, 250 DPS. I will focus on the GP -> EA -> IA transition, since that is the bulk of the argument.
We will use an army space of 30 as a common multiplier for 6 and 10 unit spaces (for 5 horses or 3 tanks respectively). It won't let me insert a chart... so work with me LOL.
HP / DPS / 30 unit spaces / Total HP / Total DPS / %HP increase / %DPS increase
Lancer: 5940 / 130 / x5 / 29,700 / 650
Cuirassier: 6480 / 140 / x5 / 32,400 / 700 / 9.01% / 7.69%
Tank: 11,000 / 250 / x3 / 33,000 / 750 / 1.85% / 7.14%
As you can see, when factoring in unit spaces tanks take up, the %HP increase is actually marginal (1.85% for IA). The %DPS increase is respectable (7.14% for IA), but no different than previously (7.69% for EA). Hence, some players purposely opt to NOT upgrade the cuirassier to tanks until much later in IA.
Once again, I agree with the call for loot and medal modification. However, I disagree with the numbers being presented for heavy cavalry. I upgraded my tank early in IA for one primary reason: increase range, which means I can take down defensive structures faster
PS: If you look up 'heavy cavalry' on the wiki, the base stats for the standard tank is as I presented. I DID NOT alter these numbers in any way. However, I assume these numbers are more accurate after comparing with those for my French tank (minus boosts).