I think this makes sense for an advanced free soloist like Alex - but does not invalidate soling easy climbs for everyone, part of the skill of free soloing is

I think this makes sense for an advanced free soloist like Alex - but does not invalidate soling easy climbs for everyone, part of the skill of free soloing is in training the mind, keeping control and conditioning yourself with the feeling of fear. You have to work up to that, and choosing lower grades helps you build those strengths - but continuing to climb them once they feel too easy (mentally), will leave you with relaxed focus, which is of course deadly.