What I'm referring is the formula from Dungeon Master's Guide where encounter difficulty is determined by total exp of the encounter, but if there are multiple enemies then the exp amount for sake of difficulty is multiplied. So if there are 15 or more monsters, you multiply total exp of those 15 enemies by 4. So in theory twig blight, a CR 1/8 enemy, would be 25 * 15 * 4 xp so 1500 xp which would be deadly encounter for 3 4th level characters... But in practice though, twig blights are slow and easy to avoid so uh.... Yeah.
Thats what I meant, even if you have hundreds of them, if pcs are high enough level they are really easy to defeat before they ever get in range of attacking pcs.
Same way, Pathfinder 1e and Starfinder has option of "If you want to simple encounter cr without counting exp budget, you can just have multiple of same CR creature and use this table to determine cr". Table where 16 creatures is "creature's cr plus 8" which in case of stuff like... Well 16 level 1 goblins aren't really "moderate" challenge to level 8 party anymore.
Or if you want to use full encouter building rules, then by raw, if you have enough mites to give 2,457,600 xp to each of 4 party members, it would be CR 30 encounter. Even though at high enough levels, no amount of mites is going to kill players even if they get lucky with few nat 20s.
Sorry if that still doesn't make sense? I'm not native speaker, but I really should practice my english grammar. It has kinda gotten rusty since I spend too much time in chats

But what I'm trying to say "by RAW, the encounter building math in D&D 5e, Pathfinder 1e and Starfinder are kinda nonsensical since they assume that enough large number of trivial difficulty creatures is enough to make CR 8 encounter as if the difficulty was same as single CR 8 creature."