I disagree, but then I usually do.....
Speakers do certainly make the most difference, but do not confuse difference with improvement.
It is my view that many modern systems are unbalanced, too much speaker and not enough amplification.
To my ears this results is a lack of control, particularly at the bass end though it is sometimes noticeable across the rest of the range. Power is important but simple 'watts per channel' are not what you need. An amplifier that can deliver it's power into the difficult load thay many loudspeakers present is needed and this does not generally come cheap.
Inadequate amplifiers show in different ways, dynamic compression, lack of dynamic shading, bright highs, soft bass, common problems with many modern systems.
Better speakers are, naturally enough, more revealing both of the music and the quality of the amplifier driving them. There are no real rules but personally it would be a rare system that, for me, usefully spent more on the speakers than the amplifier.