Given Tesla's track record of producing vehicles it is not unreasonable to assume they will be late with the M3 - The X was extremely late and took even longer to reach expected production levels. Additionally, it seems that EM's strategy to get the most from his employees is to set unrealistic deadlines. If I were a disinterested party then it makes sense to bake in some delays, but because I get a semi when thinking about Tesla I assume everything will be on time until it isn't.
The difference between Tesla's approach to MX and M3 was beaten to death, with detailed discussions. In summary, Tesla did not need to produce MX, they approached it as a halo vehicle, designing it in a way they did because they had plenty of time (due to success of MS) and (they thought) they can do it. With all the downfalls of this approach, it IS a halo vehicle, invaluable for the brand recognision, notwithstanding all the problems, real and perceived. IMO they did ultimately achieved the goal of contributing to the brand recognition and allure - and at least 400K reservations for M3 based on very sketchy information is a testament for this achievement. It boils down to reservation for a TESLA at $35K.
They do not need convince people that Tesla has most innovative automotive business any more. It is an accepted fact. With M3 platform, they need to get to 10x of the volume of MS, and the main target throughout the design is its manufacturability and capital efficiency (increased volume brings capital in, instead of capital being required to scale up). Unlike MX, the schedule is paramount because of the GF which belongs not to a supplier but to Tesla, and will be producing huge volume of batteries that must go into cars. Being late with M3 in its consequences just can't be compared with being late with MX.
So analogy IMO is just not there. There are clear risks with Tesla execution of M3 program, but I do not think you can glean anything by this comparison.
The problem is, that although all of the above IMO is a reality, not everybody investing in Tesla is recognizing/acknowledging it. I personally think that anybody looking into this analogy is divorced from reality of what's happening at Tesla. The sad part is that if majority of investors are adopting this analogy, they are creating another reality - related to the SP. So we have two divorced universes: reality of M3 program at Tesla vs. reality of market perception of it and what it means for the SP.