Alright, found something that solves the problem, with thanks to this post and adding some timeouts to the functions, I’ve gotten a replacement for onTabReady without breaking anything.
JIRA.bind(JIRA.Events.NEW_CONTENT_ADDED, function(e, context, reason){
if(reason == JIRA.CONTENT_ADDED_REASON.pageLoad){
setTimeout(function(){
actionButtons();
accordion();
}, 3000);
}else if(reason == JIRA.CONTENT_ADDED_REASON.panelRefreshed){
setTimeout(function(){
actionButtons();
accordion();
}, 3000);
}
});