It's underappreciated how much work and scheduling effort is required when access needs to be maintained throughout a complicated, multi-infrastructure, multi-street project.
It's also underappreciated that even under the best case scenario, access rarely can be maintained 100% of the time, particularly all modes of travel.
I think what Marda Loop demonstrates it is sometimes really hard to separate the politics from the project. While I understand the business frustrations of construction, some of the loudest voices didn't help themselves by stoking a much more widespread and out-loud perspective that Marda Loop is "impossible" to get too, discouraging even more visits. The construction isn't what did this - Marda Loop has long been "impossible to get too" and "under construction" according to the average discussion about the area, yet thrived anyway - it was the complaining and constant news articles about it that probably had the biggest impact.
That's not to say there's not improvements that can be made to construction processes process or that impacts weren't real, but I think the complexity of this kind and scale of streetscape project will always lead to frustrations, regardless of how it's phased.
Maybe as a test, someone should do a blue-sky project post-mortem to see what you'd need to change in the engagement, procurement and execution processes of the Marda Loop streets projects to complete it in a single construction season instead of 3 or 4 years. My guess is you could probably do it in one year with several times the budget, no public engagement, and way less effort put on maintaining access to businesses. The complaining businesses might find those trade-offs harder to swallow than what actually happened though.
In the end, Marda Loop will (somewhat bizarrely) have some of the best walking infrastructure and sidewalks in the whole city which will permanently benefit the area's attractiveness, access and retail environment. The upgrades are already being well used by the unique-to-Calgary wine bar / nightlife district that's popped up on 34th Ave, plus an infinite % increase in strollers and young families walking around with children on the wide pathways, that before were completely excluded from using the area due to substandard everything related to walking around and dangerous traffic behavior everywhere.