I have recently observed no matter how good your TA is, it doesn't always work on alt cos most alt price direction is impacted by BTC price.
When BTC is up all other coin move up. So why spending time on doing technical analysis on alts when doing it on BTC gives you a potential clue of most assets price direction?
Technical analysis of Bitcoin doesn't even come of with 100% either which makes it TA is highly unreliable when it comes to short-term market movements, I understand that your point of we should only focus on analysis of Bitcoin instead of wasting time on altcoin but you also need to understand the fact that not everytime the movement of every altcoin is proportional to Bitcoin and even it often end up inversely proportional that makes it highly inaccurate too when you are talking about a specific coin.