You have put forward no evidence say "this is patently not true” as regards the potential accuracy level of the .303 cartridge - when compared to similar others.
Conversely there's plenty of evidence, including competition results etc spanning decades both at short range & long range (e.g. 200 yard Schuetzen through to 1200 yard Match Rifle) - as to how accurate it can be when use in rifles capable of fine accuracy, rather than military rifles. To highlight the success & demonstrated accuracy potential of the cartridge isn't “pretending it's anything it isn't” - it's merely using documented results to show the cartridge is on 'a par' with many other similar capacity/calibre rounds. It's nothing special as a cartridge but neither is it the reverse.
I'm not a fan of any particular cartridge but I am a fan of accurate information. It does nobody any good, especially the OP to present old wives tales regarding the .303 being (for some unidentified reason) inherently inaccurate or below par as fact.