There are many factors affecting office growth -- of course the biggest is the remote work thing. But there is also AI which will put a downward pressure on hires in many office career fields. Computerization alone has decreased the needs for hires -- many tasks that used to require warm bodies can now be handled by one person instead of needing 3 or 4. The office matrix as it applies to downtown growth is likely going to be limited to single person or small groups of professionals -- doctors (especially specialists), dentists, lawyers, realtors, architects and engineers.
I don't see much residential rising to the status of "legacy" buildings anymore with very few exceptions -- the Parks, Qualico's build-out, ICE II are the most notable. I know I get flak for repeatedly saying so, but there is a rush by some developers to build downtown as cheap as possible -- maximum profits:minimum effort.
Mixed use is going to be the biggest potential for legacy projects in the fields that you have mentioned -- again the Parks, Qualico, and ICE II. That said there seems to be a convergence on a developmental attitude to avoid the "mixed part" of mixed use and to build crap with the call signal "what a good boy am I"
Otherwise the Legacy Potential rests on Arts and Entertainment Projects, Sports Edifices, and Post-Secondary Schools -- these are the types of buildings we should be heralding for downtown -- so far the architecture in these areas has been above par.