Now that we’ve got the ability to associate a class per team without paying gems or waiting, wouldn’t it make sense to have unique talent tree selections per team? For instance on a purple team, you would probably want bonus purple mana on purple gem matches but on another team with the same class you may not want that specific “branch”. Currently, if you change 1 branch it applies to all teams with that same class including your defense team or Guild Wars Defense teams so setting up defense strategies isn’t very intuitive.
I’d agree only if it were then also possible to reset your talents back to a global template that you could set (I quite like this idea, as there isn’t currently a way to look at your Classes without selecting a team in the Troops menu) or to match one of your other teams.
GW may be another story - I personally believe there should be unique and separate team slots reserved for each day of GW, similar to Pet Rescues (which also have one team for each colour) - and for which unique talent setups would be very useful, as GW Defences are well-suited to careful planning. Currently, as you alluded to, your carefully devised defences can be ruined if you decide to try out Chaos Storm (Summon a random storm of 4 or 5 Gem matches) on your Frostmage on another team, and forget to set it back to Snap Freeze (Freeze a random enemy at the start of battle).
I suspect the Devs made a conscious and considered decision to not include unique talent trees for teams, with which I can sympathise. One of their concerns prior to free class changes/being able to set classes to teams was (I believe) the amount of time it would take to set up your team each time you wanted to change it or try something new, instead of just playing.