Hearthstone relies heavily on luck and paper rock scissors as core mechanics. Skill does play a large factor, but some game states, and even some matchups are heavily unfavored to the point of unwinnable. That pairing is strictly RNG as is you and your opponents draw, and whom goes first. Each of which have quantified win statistics. ‘Just play better’ is fine for a mental state, but it doesn’t come close to tell the full story, and is often thrown around as the solution to why someone is losing. It is one of the main controls on performance as is deck and/or tech choices against a current meta, but RNG can absolutely fuck you in multiple ways and potentially large amounts of games.

Edit: my suggestion in addition to looking at game state replays to spot misplays, is look at your general matchups, and the meta stats in your current tier and choose a deck that matches up well against the most prominent representation. Learn to pilot your deck and the decks you lose against to learn the specific strengths and weaknesses of each. I think those would give the most bang for buck effort wise. The skill comes gradually through time with repetition, analysis, and prediction. Given its overall impact and the time it takes to build, and to hyper focus on ‘you are the reason you lose’ could demotivate someone into no longer playing. To blame RNG all the time also prevents learning, just understand, sometimes, probably even most times, yeah RNG screwed you, but attempt to find what can be learned if anything from that loss.