then you might as well dismiss any opinion on any hero’s balance because no-one will know in full detail what another person knows 
she may be more likely to live, but at the price of giving up whatever area she claimed. an area claimed by a turret nest is claimed until they’re destroyed or until sym moves them while she can operate elsewhere.
tracer gets multiple angles for her team, not on her own.
preemptive or not, it is still a significantly long time esp if changing between high ground and low ground. whereas sym tp’ing for 1. or 3. likely doesn’t take as long on most maps —> don’t need to be as preemptive i.e. can be more spontaneous (flexible and dynamic) about it.
I assume by “actual mobility” you’re more talking about like an instant directional dash ability of some sort? if that is the case then I don’t really see how it’d make tp more effective tbh.
In general, no mobility will make her current primary effective unless that mobility comes with like long i-frames. sym’s primary is a sustain weapon, i.e. needs longer durations of use to get value. getting in range is half the problem, the other half is staying alive. unless she gets zarya levels of sustain, it really isn’t going to happen. yes with mobility you might be able to get sneaky angles for charge, that still doesn’t mean you’d live long enough to make use of it. Plus tp, when given enough cast frequency like old 3.0 tp, allowed that, so not sure what you had in mind that “actual mobility” would add.
my point in raising double shield (and potential triple shield) is to point out how it’s not changing much of the status quo. she’d remain excessively team dependent due to, as you said earlier, her lack of agency for getting in her effective range, and her lack of balance for her ttk on others vs her sustain in her effective range. Like the only reason why sym’s “good” in double shield deathball comps is because they inherently team pocket (absolutely cater for all the weaknesses of) her w+m1 gameplay.
like if we stop focusing so hard on sym’s lost cause primary, which objectively is a minor aspect of her gameplay due to its constraints and always will be, and focus on making the majority orb + tp portion of her gameplay better, we’d actually put her more up to standard, viable and healthy state.
I mean 2.0 had no mobility… old barrier was moreso only good for blocking ranged stationary shots (e.g. widow or bastion) or blocking single abilities. it wouldn’t get you access to hard to reach areas like a flank route behind hanamura A choke when the enemy is holding the choke (ultimately leaving 2.0 sym with nothing to do except spam orbs for ult charge until the team pushed them away).
old 3.0 tp cd mechanic was a very decent deal:
I often ended up using tp for 6s which left me with 6s down time on it. e.g. https://www.reddit.com/r/SymmetraMains/comments/al4qeu/reaper_relishing_in_buff_and_new_skin_me_yall/?utm_source=share&utm_medium=web2x
given that orbs at 15m give enemies 0.6s to reactive dodge fired orbs and at 20m it gives 0.8s, orbs do need a speed buff.