How to make it count for putting out fire before it started?

Background:

Our team inherited a set of products which are full of spaghetti code and bad design. We are currently building a high visibility and high impact project based on the backend of this system.

Although the main project UI goes on-track, some critical backend design flaws will hinder product performance and reliability within a couple of months - maybe close to or right after official product launch, which will turn our whole effort into a joke since we have executives' eyes on it.

My progress this year so far: (besides my roadmap item commitment)

• 1. Identified a system hotspot, finished analysis & design, and convinced our EM to rewrite this module (currently 95% finished by a junior engineer.)
• 2. Rewrote 1 foundation module to eliminate legacy design flaw (ended up with less code, less complexity, same performance, more system reliability.)
• 3. Design and rewrite another foundation backend module to address legacy design flaw & unblock development of the next milestone
• 4. Leading on technical design and discussion of a re-architecture for the overall backend end to end flow. (simplify design, improve performance)

NOTE:
- I tried to delegate 2 & 3, but no other engineers can do them after a few try since it's too tightly coupled with the rest of the system.
- our team lead is championing for all these work, which is how we are able to make room for them

Benefit of these work:

• accelerate other engineers' work in the system
• cut clean with the legacy system design flaw, improve product reliability and performance
• ensure our team's win on the high visibility project that built on top of this backend
• easier oncall for the short run or long run

My questions:

• In terms of performance review, my manager thinks this is better engineering work, while I think is closely tied to the success of our main project. What kind of evidence do I need to convince him? (My EM is not very technical)
• From his tone, I sense he thinks better engineering work in considered "lower priority contribution". Is this true? How do I communicate the importance of code/design quality with him?
• I'm trying to reach the staff level promo, does this initiative demonstrate any trait for the next level? (I'm not doing it for promo, but my EM's neglect on this makes me pretty frustrated because refactoring and rewrite is such tedious and painful work... I want to make it count)

Thank you!