This sounds like a good plan except that is it not true that the direction of development now is on layer 2 rather than on chain? I think the size is still a problem so they would like to restrict it on chain like that and keep those 100k transactions all on Lightning.
There is simply no way that transactions are done entirely on lightning or on layer 2. That is unrealistic and makes Bitcoin completely useless and which is why I've criticized repeatedly on the fallacy of having a limited on-chain capacity and banking on off-chain TXes to sustain the TX volume. We absolutely need a capacity increase in the future to even think of mass adoption. Again, 7TPS is ridiculously small and lightning network isn't (and should not) be the solution to the problem.
Again, the problem we're looking at right here is not to ensure that we maintain the same level of security. The whole point of PoW is to make it more expensive to attack the chain than be honest. If there is a substantial security decrease but we're still looking at a huge discrepancy between the profits from an attack vs profits from mining, then there is no problem.
I do not disagree that on chain capacity needs to be more but just from what I can gather from my own observations that everybody seems to be building on L2, as long as,,, on L1 when they finalize the channels they can be sure of security and permanence. Which is still the biggest strength of Bitcoin as opposed to Ethereum and others all popularly using L2.
I do think the level of security is high enough that it does not need to be much higher, just as you say to make it too expensive to attack. But it is not just about hashpower also but the diversity of hashpower that is important.