With more focus on HTHS the analogy only becomes: ripping the carb off your supercharged 383 and putting on new-old-stock of similar appearance and slightly more cfm, then enlarging main jetting and loosening an idle screw and calling it good. Which can work for 30 minutes or 30 years, but no, it ain't necessarily so.
The Mobil1 ESP x2 0W-20 for example appears to be thicker (depending on perspective) than the two 5W-20 oils mentioned last. HTHS values are virtually indistinguishable here and for certain areas or higher shear rates the behaviour is different again. xW-30 up to 3.2 in HTHS would be a reasonable alternative when questioning 0W-20 in summer heat.
I wanted to chime in about another good, thick 0w20 which is Valvoline Modern Engine. KV100 is 8.8 and while the HTHS is not listed on the PI sheet for this specific oil the other Valvoline full synthetic 0w20 oils are listed as having a 2.7 HTHS so I would surmise that Modern Engine would be similar if not the same. I like the fact that this oil was specifically formulated for usage in direct injection engines.
HTHS viscosity is the number you ultimately want. In most cases, the HTHS will be higher when the oil also has a higher KV100, so if there is no HTHS data available then KV100 is better than nothing to compare hot viscosity. A lower KV100 will most likely also mean a lower HTHS viscosity.