I dunno. I'm ok with every country having their own thing. Merging leagues means 99% of the teams in those smaller leagues end up falling off and get hurt because they no longer get any revenues from the few times they played the big teams.
The big difference is it is all still based on merit of course. It's inevitable that teams will grow to dominate over time and the bigger will grow. Everything should be done to help promote a level playing field, but what can really be done? TV viewership is balanced with the biggest still getting more though and slowly widening the gap, just not as quickly as in Spain. And then they get big bonuses when they get the added bonus of CL football.
If you want a truly level playing field, then pretty much the whole business has to be reformed. Salary caps for all players and clubs being the same across every team in the league. Transfer spending caps being the same for everyone. Promotion or relegation means you have a different amount to deal with now. Change laws regarding profiting off football clubs and ensure the money stays invested in the club and the community as a certain percentage being guaranteed non profit. Dead even TV income. Any money from European competition goes directly to the league to be shared equally, and the competition being mainly pride based with the money not going directly to you, but everyone from your country. Over a long period of time eventually the smaller clubs will earn enough to be able to meet the salary cap that the top clubs could already meet, and so everyone would have an equal financial level in terms of salary and transfer fees. So then the edge that clubs attempt to get with money would be investing in facilities, education etc which would be for the betterment of everything anyway. But the big thing is then it'd still go the way it is now. You'd still have a super league eventually, by way of the premier league becoming it rather than across Europe as you'll still have that gap between leagues. It's impossible to have a level financial playing field between countries, and its honestly not all that relevant. This one definitely falls in the "sucks to suck" area IMO. It would be great if every league had equal chance to be at the top, but why would England, Italy or Spain get it and not Netherlands, Portugal or Turkey?
Basically any sort of change to level the impact of financial disparity on the pitch could only be done within a division, would require a very long period of time, and in reality would still be dominant teams, just through their facilities and not their salaries. Combining domestic leagues probably doesn't do much for most of the league and just pushes them down to lower divisions, aside from the top few who would be benefitted.
Anyway, if you have just 1 cross border European domestic structure, does that really benefit anyone but the top? It's much more beneficial for a small European club to get drawn against a European giant. And in the grand scheme of things, you'd get such a big disparity between the top clubs and the rest. There's no longer a competition that gives you this big financial boost if you do well domestically. It's all just the 1 competition, with less chances of upsets eventually occurring. The reason it was even before was because football didn't spike financially, there were laws that meant players couldn't leave their domestic league until the age of 27, and only the champions qualified for the European Cup. None of that exists anymore so dominance and a growing difference financially is inevitable. At least this way, countries can control a level playing field within their own leagues and still maintain that fanbase, and they will always have their routes to the Champions League to ensure that the best players at least aren't fully hoarded by 1 league.
