Those teams you listed did
qualify to get their face pounded in by the big boys, through a series of winning increasingly lucrative qualifying rounds. Let's take a look at how these teams stack up and how they got to the group stage.
(Recall: Direct qualifiers to the group stage include the champions of leagues ranked 1-12, runners-up from leagues ranked 1-6, and 3rd-place teams from leagues 1-3, plus defending Europa or CL champions depending on their league finishes.)
- FC Basel (current
UEFA rank #19), 1, -5: direct
Group Stage qualification as Swiss champs (association ranked #12)
- Ludogorets (
#83), 1, -8:
2nd Qualifying Round as Bulgarian champs (assn #29), beat teams ranked #344, #190, and Czech team Viktoria Plzen (#43)
- Dynamo Kyiv (
#26), 1, -3:
GS, Ukrainian champs (assn #8)
- Celtic (
#54), 1, -9:
2QR, beat Lincoln Red Imps (#407), Astana (#137, who of course later beat West Ham), and Beer'Sheva (#205)
- Rostov (
#146) 1, -6:
3QR as Russian (#7) runners-up; beat #38 Anderlecht and then Ajax (#30).
- PSV (
#33), 1, -4:
GS (assn #10) as Eredivisie defending champs
- Warsaw (
#74), 0, -12:
2QR as Polish champs (assn #18), beat #335, #249, then defending Irish champs Dundalk (#359)
- Brugge (
#47), 0, -8:
GS (assn #9) as Belgian champs
- Zagreb (
#82), 0, -8:
2QR as Croatian champs (assn #17), beat #297, #237, and then Red Bull Salzburg (#48)
Few of these guys are pushovers. Some are even semi-powers: PSV and Kiev reached the R16 in the Champions League last year, Basel too the year before, and PSV took Atleti to PKs after two scoreless draws. Meanwhile, Besiktas (#62, from Turkey) is ahead of Benfica in their group, Copenhagen (#82) is ahead of Porto on GD, it's not hopeless from those from the lower leagues.
Of those 9 you listed, 3 clearly belong in the group stage (Basel, Kiev, PSV), 2 are borderline (Brugge, Celtic), and 4 are foreseeably hopeless (Warsaw, Zagreb, Ludogorets, Rostov). But even among the hopeless group, Rostov beat two top-40 teams, Zagreb beat the defending Austrian champs, and even Ludogorets took out a quality team in Viktoria Plzen. Only Legia Warsaw won the cupcake-draw lottery, among the whole of the 32 group stage teams. And as for Rostov, their compatriots, Russian champs CSKA Moscow aren't doing much better, on 2 points, -1 GD.
So where do you draw the line? Consider how incredibly stoked the fanbases of those 4 how-did-they-get-here teams are. How much their fortunes are rising and the ROI for their owners is skyrocketing with that group stage cash. Teams making the group stage are guaranteed EUR 12M, plus 0.5M per point they earn in the stage, plus a weighted distribution of TV cash. That's a jackpot to these teams, especially the ones outside the Euro zone (Kiev, Rostov, Ludogorets, and Basel too not that it matters to them).
The underperforming mid-major powerhouses (Basel, PSV and Kiev) would clearly still be in the group stages even in a rejiggered alignment. Sometimes clubs have down years. PSV ousting Manchester United last year, that's the stuff of legends - that's a big argument for
why even have a champions league in the first place. They won't pull off miracles every year, but they're the teams from whom miracles are possible. When they pull it off, it's because they're the "whole is greater than the sum of the parts" teams that have just gelled despite a deficit in natural talent relative to big-5 leagues. And those 3 netted EUR ~30M each the last 2 years for their respective R16 runs
What would be an improvement? More teams in the playoff round, with more #4s and some #5s from the uber-leagues? I could maybe support that, but it would seem that that would just reinforce and institutionalize the financial advantage of the big leagues, rather than dangling a carrot for smaller leagues that is within plausible reach. Being a mid-major league champion who earns their way into the big-boy rounds should be among the highest achievements these guys can aspire to. Meanwhile, it's way more exciting to them than it would be to mid-table teams in the EPL, whose fans would rightly feel like they were being awarded a prize they didn't really deserve.
Basically, I'm fine with a handful of minnows in the group stages