yah i understand. but for me, usually i see them as seperate currency. so i try my best not to bother too much about the rate, like my net worth it is increasing or decreasing due to varies exchange rates, i will see as raising the amount of alt. i know it is not a wise move but sometime i put some $$ into an alt, i just let it be there and never convert back to fiat or btc.
Definitely an issue. Bitcoin is the only widely spread crypto, so everything else has to be denoted in BTC value. Because if you ever want to make an exit, you're converting to BTC (or to fiat, but that would be based on BTC's value as well).
but to be honest, if were to follow how you think it is, the best way is at the start invest in alt coin at the start, when it rise and then exchange back to btc before it fell. then you dont even need to keep alt coins at all. maybe becuz i know i am not a gd predicter in market, so i end up keep it all the while, easier for me.