As someone who worked on legal matters for 3-4 years in the Government department I worked in, let me take you through what the PL/UEFA's legal team would hone in on.
'...a club shall not enter its senior men’s first team in any competition...'
1. The clubs publicly announced their entry into a new competition. Statements were made, and published.
2. The new 'European Super league' (the Competition) issued a press statement to the effect of the formation of the new league, and its initial constituent members.
3. Notwithstanding the 'no promotion or relegation' scenario, it is a competition based on two opposing teams competing on a field of play.
4. In terms of semantics, the ordinary legal construction placed upon the word 'shall' is directive, not optional. 'Shall not' is therefore directive.
The above four points prove beyond any shadow of a doubt that the European Super League' was a competition with 12 founding members and its complement to be increased by invitation to other teams.
You don't have to kick a ball, or have any fixtures or dates put into a calendar for something to be classed as a competition. The youth teams that I ran had to apply to the local Sunday League youth association (affiliated to the County FA) for admission each season. You were then accepted ever before fixtures or dates were set in a calendar (obviously - you cannot put the proverbial cart before the horse!). So your claim is demolished in one simple point.
I hope the foregoing clarifies things for you.