I think the realistic answer is that we can’t guarantee that every subnet will always have a ~2 second update latency, because every subnet has bounded capacity, and if the loads grows big enough, it will exceed what the subnet can do and certain messages have to wait.
I hope that the community will adopt the cycles cost adjustments that DFINITY proposed, which may lead to reduced load, especially in the type of workload that we now see incur a lot of strain on the subnets. This would make it less likely that subnets are overloaded. These changes are easy to make, so they can happen as soon as the ICP community decides that they want this.
Separately, the replica improvements are being worked on and can hopefully increase the capacity of each subnet, so that may help in the coming weeks.
Finally, adding more subnets (topic) would increase the capacity of ICP. Out of curiosity, do you want your canisters to run on the european subnet, or could you migrate to another subnet? If you really want a european subnet, perhaps it would be good to mention that, maybe we should explore if a second european subnet should be created.
Finally, canister migration would help fully distribute load across all subnets and should remove the problem of highly loaded subnets (as canisters would just move to a quieter subnet). However, this will be in the order of months, not weeks.