/laugh sure, I'll bite.
First off, and the most stupidly obvious, there are no downsides to not participating in missions. While you could argue the fact you're not getting that content, you are not actually losing anything from not participating vs. the event not happening at all. Arguing that it doesn't 'feel good' would be like Riot having an event that gave you 1 RP per game, and having everyone whining that they aren't getting enough RP. Seriously, I shouldn't even have to say this.
But even if really you go past that, and argue that the post was about poor design... the missions themselves are intended to not be the core experience. The intention is not "I'm going to play 50 games to complete this quest", it's "I'll get rewarded for playing the game well." It is not "I'm playing 50 games to get a reward", it's "I'm rewarded for playing these games that I'd play anyway."
With the missions, you should be able to get them by just playing the game as intended. (With the small exception of support mains and the CS quests, but this also came out alongside ARURF, which makes for the even smaller exception of support mains that don't play urf- and even then, only one of those quests, veig level 2, are unrealistic for supp mains to get. if you really want the content you can grind Veig level 2 in ~2 hours of bot games. BTW did I mention, they get the fastest completion of the blitzcrank line.)
The other monetization things are worth the cost themselves (Maybe with the value exception of Good Orb- technically it's worth it RP-wise for a champion shard, but most people that dump money into the game don't want one, and most don't care about summoner icons either. Ward skin shards are k though.) 3 great orbs is effectively a mystery skin (With, I believe, a chance at legacy skins) alongside a chance for Gemstones + Dreadnova Darius. Not to mention the fact it can drop itself. Slightly more expensive than just purchasing a mystery skin, but you can do it for yourself + that chance for legacy + the flexibility of either rerolling or just using the orange essence = profit. Mega orbs aren't quite as good, but they're effectively the same thing, but with a chance for two gemstones, but they always give you legacy skin shards, which is useful if you're going the orange essence route and want some skins that most people don't have.
The mini dungeon pass is almost worth the RP for the ward skin alone (650 vs 640-Unless the daily missions aren't worth the 10 RP, it's valuable itself and only $5 for a cool ward+keyfrags/skin shards is fine) making the daily quest only an added bonus, and the dungeon pass is already worth 900RP before you consider the good orb (150 RP), a gemstone (Even worse case scenario it acts as a chest + key at 195 RP, but most people would probably pay way more for a guaranteed gemstone.) Which puts the mission costs at 250 RP total, or $1.92- with the cheapest conversion of RP:$, and the missions, which you should get naturally and give you enough tickets for enough good orbs to get you a reroll, essentially a mystery skin.).
So effectively, there's nothing wrong with the event, and it's not actually hurting anyone by existing. It's effectively just giving free stuff (A summoner icon and a skin shard- ~$4 of value) and offering people who want to put money into the game more interesting ways of doing so, and these complaints about how it's not 'enough' are self-entitled brats that want everything handed to them. All of my main points (minus the numbers) should be something that is severely obvious to anyone. Seriously, this wasn't worth the twenty minutes to write/calculate everything, only further evidenced by the lack of response to this post.