After a few days I think it's clear what some of the actual biggest issues with the system are.
- The ELO system is not compatible with the streak based allegiance bonuses. When an ELO system is working correctly (SoT's hasn't calibrated yet) players should theoretically be winning about 50% of their matches. This is generally fine, but this kind of system works directly against a system such as streaks- once the system has settled this means the only people really going on streaks are going to be those who obviously aren't at the correct ELO. Anyone who's played a game with SBMM knows what the consequences of this will be.
- Higher ELO will cause awful matchmaking times. This often becomes a problem in games that use it. Poor matchmaking times seem to already be an issue for most players in general right now, and the estimated matchmaking time is completely unreliable.
- We have no insight on how the ELO system actually works. Some players seem to think it may actually be a system where only wins are counted and not losses- this would prevent people from de-ranking (which is incentivized due to the streak system) but is an equally awful thing and I'm really hoping Rare has more sense than to design it like that.
- The preset mutual invasion locations (north of Smuggler's Bay and south of Flintlock Peninsula) are poorly chosen, with environmental hazards (intense waves, fog, volcanoes) having too much of an impact on how fights play out.
- The tendency for kegs to spawn in the Barrels of Plenty in the mutual invasion spots is way too high.
- I don't see the necessity of locking the option to fight bigger ships behind streaks. I understand it may be this way to prevent new players from accidentally triggering it, but it's just kind of silly.
- The incentive for carrying loot and opening yourself to invasions (rather than diving) is too low. Players who wish to open themselves to invasions while running normal emissary flags (merchant/gold hoarder/order) and stacking "normal" loot should have an incentive to do so, in order to create emergent encounters on the seas.
- Players should have a way to skip the invasion cooldown timer, so that they can opt-in for PvP immediately without having to dive (if for example they are stacking loot or flags).
- Losing battles and having to resupply is extremely time consuming and tedious. Opting to skip this will put you at a serious disadvantage since most players are going into this mode with insane amounts of supplies.
- Beginning battles with both ships nosing at each other full speed is terrible. It feels especially bad in solos where you need to choose between helm and cannon as you are immediately forced into a broadside.
- Solo sloop battles quickly devolve into wars of attrition if both players are playing at a minimum level of competency and there isn't a seriously massive skill gap between them. There is no real punishment for simply running away all fight, and the game mode has no timer or mechanic to prevent this- essentially rewarding whoever can out-patience the other person first.