I’d be fine if they ended up selling cosmetics from events after two seasons (which I hope is six months). If you played the event, you had the chance to get it for free and wear if for a while before others. They could even just sell the ten tiers as a bundle.
Perhaps the way you worded your statement is confusing me, but are you suggesting seasons should be six months, or that two seasons should approximate six months? I do hope it’s the latter 
As I and others said previously: It isn’t necessarily about wanting the cosmetics themselves, but rather having something to do. Especially now, a week without an event pass, what is there to grind towards? Of course you can make the “If you genuinely enjoy the game, just keep playing for fun!” argument, which I wholly agree with, but that doesn’t lead to player retention at all, and this is provable. FOMO is an awful concept that generates momentary hype, but I feel as though 343i is late to the party on this one, especially when you consider that subtle story hints are being dropped in these events, which I wasn’t even aware of until recently. Making this content permanent in some way should be a goal; Tie it to commendations, challenges, etc.
I imagine the Fractures will come around repeatedly. If you missed Tenrai the first time, the second time around they’ll add 30 tiers, so if you’re new there are 60 tiers to unlock. No FOMO - just a little behind.
I like this solution. The system of only having ten challenges/tiers to unlock per event period is a concept that needs to die for this to work out for the consumer, imo. Be pro-consumer on the free stuff and you’ll retain more players.
I don’t want to buy the unlocks because I already have them. I certainly don’t want to replay the events. Why should people who missed out get to unlock old stuff through events over those of us who already completed the events getting to unlock new stuff? The new stuff is also available to those who missed out on previous events.
Toxic take imo, microtransactions and FOMO are something I wish I had the budget and capacity to study, as I hypothesize they’re directly correlative with anxiety and thus constitute predatory marketing. This is a moot argument considering you can chose just not to care, but for the obsessive this can be hard to accomplish. My thought process is: Why sit on perfectly good content that has a measruable demand when you could be using it as a gateway to bring in new and former customers? A great example: If they were to bring back Tenrai, they could also bring back the associated Chonmage microtransaction pack at the new reduced cost that armour sets are now, and perhaps run another, new armour variant alongside it. This is the simplest, msot effective answer to this dilemma however you look at it imo, hence I believe it will inevitably happen, probably around the beginning of Season 4 when I believe the game itself will have the soft “restart” I see people talking about occasionally.