Now the debate should be: is BTC losing ground long term, or just indicating another bearish move lower for crypto in general.
I'm not convinced the two are mutually exclusive. While we've seen a nice recovery lately across all crypto, all the indicators suggest an overall slowdown in "new" interest in crypto. See, in particular: https://cointelegraph.com/news/pro-btc-wall-st-analyst-urges-not-to-buy-crypto-now-despite-recent-rally
Because BTC is what most people buy due to awareness and Coinbase's limited menu, it's an indicator of overall crypto interest. That being said, I also agree there's a long-term shift towards alts from BTC, esp. amongst longer term investors so BTC has double exposure there.
All this to say - some of the reasons why I'm not in BTC at the moment and instead in alts!
Very valid point, and I'd say they're not.