I only have AmEx Plat Business, so I have booked via AmEx travel to get the 5x points. (Always helpful when posters note this important and annoying difference between personal and business cards!)

While I still very much prefer to book direct, I've definitely booked via AmEx (and Chase) to increase my points earnings. I also needed some spend to earn the bonus as the AmEx is new. In the past year, as SO MANY flights have had changes, I've also had to adjust some Alaska flights due to a new itinerary not working for me. IIRC, I've been able to do this with a phone call to Alaska, but all my recent changes have been due to Alaska itself making major changes, not by choice, so that may be a factor. I'm afraid I'm not certain offhand if those flights with changes were booked on AmEx or Chase travel portal, however.

Even having booked via the portal, I am still able to do all the things I care most about online: pull up my flight in the app, add meals, change my seats, etc. I rarely book flights I don't intend to fly, however, and I usually book two one way flights instead of RT fares to reduce even further the odds of breaking one piece if I do change another.