I always find it very strange that whenever you get some silly debate like this about "yuri bait" that everyone seems to assume bisexuals don't exist particularly in cases where there is some evidence of attraction to both sexes. People act likes it's impossible that a girl would appear to be interested in another girl romantically and then end up dating a guy. This happens all the time in real life so I'm not sure why it needs to be a rule that it can't happen in fiction.
That's completely fair and bi-erasure is certainly something that needs to be tackled. But in the case of deciding if something is Yuri or not, if the character only ever dates a guy and we only see subtext with another girl is that enough to call it yuri?
If the not openly confirmed subtext relationship in Lycoris is considered yuri then I suppose Euphonium could be as well, even if there's never a girl-girl relationship beyond subtext.