For me, ‘better’ implies that it is not good now. That, for right now, there are flaws that can be immediately rectified (and that possibly should have been identified previously).
There’s a hint of blame in ‘better’.
‘Best that it can be’ takes factors into account. It allows imperfection. It has faith that there has been real and honest work.
Evolution will happen. Growth will happen. ‘Best that it can be’ …with an inferred additional clause … ‘for right now‘
No blame. Acceptance of reality and an understanding, and encouragement, of constant change.