All things Lilligant can usually do better with better results thanks to Chlorophyll.
And if we just let any Pokemon on the VR be C rank for simply having strong priority and wallbreaking ability or can theoretically beat a top tier, C rank would be filled with more Pokemon than rest if the rankings combined. Why not add Infernape and Conkeldurr and Pawmot?
Plus Spore absolutely does play a part in breaking Pokemon. A Pokemon that otherwise tanks Breloom’s hits can be put to sleep for multiple turns where Breloom can do what it wants.
And an extra kicker, if your opponent still has Tera, what exactly are you going to do against Roaring Moon? Or Kingambit? Hell what about Dragonite with or without Tera?
I disagree with the notion that Lilligant, or any grass/fighting type for that matter, is strictly better than breloom in every aspect, with or without spore. As other people have stated, lilligant’s revenge killing capacity is reliant on sun being up- something you can’t rely on as much as you can rely on breloom’s mach punch. It’s revenge killing potency in this regard is why I feel breloom is defined by mach punch even more than it was defined by spore— and why choice band breloom was it’s best set even before the sleep ban (and it certainly is today).
As for why it deserves to be C rank unlike other wallbreakers that can “theoretically beat a top tier”, breloom simply has the edge in raw damage, to a level which can quite frequently come in handy for certain damage thresholds- for instance, with the example you brought up:
252+ Atk Choice Band Technician Breloom Mach Punch vs. 0 HP / 0 Def Roaring Moon: 428-506 (121.9 - 144.1%) -- guaranteed OHKO
252+ Atk Guts Conkeldurr Mach Punch vs. 0 HP / 0 Def Roaring Moon: 302-356 (86 - 101.4%) -- 6.3% chance to OHKO
that let it act as a powerful revenge killer and stallbreaker, since between blissey, ting-lu, clod, and bulky waters like mola and dozo, stall teams have very few options when it comes to things that can switch into both cc and bullet seed from cb breloom.
However, even without spore, breloom still sets itself apart from other slow wallbreakers thanks to an incredibly powerful priority option that enables it to not only revenge kill the numerous setup sweepers and faster pokemon of the tier, but also function as a late-game cleaner— something that sets it apart from first impression users lokix and slither wing, who need to switch out each time they wanna use it and as such can’t really clean up a game if they’re the last one alive even if they might trade more effectively.
Mach punch also doesn’t rely on the enemy using an attack like sucker punch and thunderclap do, so unlike kingambit or raging bolt, you’re not reliant on mindgames to deal with threats that outspeed you. That’s not to say that breloom outclasses either of these mons by any means— but it does mean that Breloom can offer a greater degree of consistency in certain situations, and it also gets to really mess with the mons mentioned above, since being able to act before these moves (unless raging bolt runs enough speed investment to outrun adamant breloom, which it rarely does) lets breloom deal damage to them without actually being hit by sucker punch or thunderclap.
Now, with the loss of spore, the choice for breloom’s 4th moveslot is generally between rock tomb for zapdos and enamorus, or bulldoze for gholdengo and glowking, and I think this is truly up to what the team needs, but I don’t find other options to provide the same value in that last moveslot. While you could, in theory, run something like tera ice tera blast to hit gliscor or lando, I don’t find such options to be worth giving up the potential extra power of tera fighting mach punch.
Overall, I think breloom should
remain in C rank due to it’s choice band set being able to function as a wallbreaker, revenge killer, and sweeper all at once, to the point where it’ll always contribute something in every match you bring it to.