In short, I don't believe there is such beast as ideal machine/grinder...
I don't recall a moment where any upgrade had led me to a significantly higher plateau (except when I first started out with a Gaggia SBDU and upgraded to levers), but I did have moments where I got progressively better machines that are easier to live with.
If you are concerned with shot quality, my biggest take away was that as long as you are above a certain budget level, the law of diminishing return kicks in really quickly, and hard (I may be biased, but to me lever machines seem to get you there quicker). Shot quality can/will be different but it's hard to claim objective superiority. The difference is usually subtle anyway and we're much better off focusing on the other aspects (techniques, beans etc).
Since the shot quality is largely the same, the user experience (ease of use) and shot-to-shot consistency (forgiveness factor) become much more important as you go up the tier. That's my 2 cent at this point.