Andrew RT Davies criticises Plaid Cymru for attending a rally with a message of support by Kneecap.
The event, organised by Yes Cymru and All Under One Banner Cymru, was held in Barry on Saturday.
Organisers say the march is a "celebration" of how far the movement has come.
Gwern Gwynfil was axed on Monday, but defended the organisation under his stewardship.
Organisers say the number who took part showed "the tremendous increase in support" for their cause.
The majority of train services were suspended in Wales as part of nationwide strike action.
David Buttress, who has been appointed by the UK government, has a history of criticising ministers.
Siôn Jobbins says Scotland's push for an independence referendum means Wales must be ready.
