I have sympathy for Celtic. UEFA are happy to let these mis-matches continue, and even get worse because they are not interested in controlling the mega rich clubs and football will suffer in the long term. You often hear how important it is to be in the CL for all the revenue it generates. But there are certain clubs that are spending even independently of the CL revenue! How can a club that attempts to keep to anything like a proper financial business model hope to compete with such unlimited spending power?
I also laugh when I hear the pundits going on about how noncompetitive the PL teams are in the CL, when the most basic and obvious point is that if a team doesn't have to put out it's 100% strongest team in it's respective league, it will always be strong in the CL. The Spanish clubs don't need to be strong every week, and nor does PSG and Bayern (don't know much about the Italian league to comment on that). What makes the PL great is that there are a lot more competitive games than in those other leagues, so saying our teams aren't as good as those "top" CL teams is not comparing like with like.
There's an obvious paradox with what you're saying: for several years both Man Utd and Arsenal could afford to rest key players for a stretch of games, be it Man Utd giving Wes Brown and/or John O'Shea a run of starts or Arsenal giving Junichi Inamoto a game to keep the Japanese tourists visiting Highbury in order to keep their key players rested for the Champions League games - and the only thing to change this was Roman Abramovich showing up at Fulham's second club.
And let's be honest here, for years on end the top four was the same four teams in roughly the same order every single season, and the only thing that broke the stranglehold that Man Utd, Arsenal, Chelsea and Liverpool's G14 tribute act was City also finding an obscenely rich benefactor that meant that mathematics was against the five of them getting a slice of Champions League cash. To put it another way, on Old606 Man Utd, Arsenal, Chelsea and Liverpool were referred to as the Sky 4 for a good reason - but now all you have to do is swap Arsenal out for City and the situation is exactly the same, and by complete coincidence this is being reflected in Arsenal's current portrayal as a fallen giant/feeder club for The New Sky 4.
Having a couple of teams buying their way into the VIP area doesn't make a league stronger, it just exacerbates the problem as it increases the number of teams able to stripmine teams which threaten their position of players. A decade ago we had Keane and Berbatov pinched in the space of a summer while Villa got it even worse as half of their team were spirited away by the Manchester clubs, but now we have a situation where teams can be dismantled by several teams at once, as Southampton are only too aware of.
I doubt many Ligue 1 fans would suggest that PSG having more money than the rest of the league combined has made the league stronger, they'll say that an upstart club is buying success while making Ligue 1 a laughing stock, and it;s not helped by PSG creating a Narrative where they are now The Most Successful Team in French League History...while hoping that nobody points out their trophy haul is grossly inflated by Coup de la Ligue wins, and as things stand they have less league titles than Lyon, Monaco, OM, or Saint Etienne.
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