Methinks that this is an oversimplified discussion. The Low speed drag polars are related to EAS, true, but at higher levels the same EAS will be beyond Mcrit, and total drag will then be the sum of the low speed and the high speed drag polars.
Below the Pressure Height where the selected speed schedule is below Mcrit, the previous arguments hold true, above that, typical flight is at a Mach Number about .03 to .04 above Mcrit, with decreasing CAS/EAS as Pressure Height increases.
Regards,
Old Smokey