If you think about it, smaller MTU will potentially increase latency, more packets to process.
When trying to push high-speeds yes, but the whole point is bufferbloat is only really an issue for low-bandwidth time sensitive traffic where that is not an issue.
Limiting the available bandwidth is not a practical solution when you cannot guarantee the size of the link, which you can never be 100% sure of on a contended network. Its unlikely to be a common problem on a good ISP with a good backhaul provider, but a cheaper ISP with a cheaper backhaul provider who has more contention, it still may be.
