I think this is a good change but Catalyst, Willbender and Mirage all need some access to an on-demand burst of quickness or alacrity outside of combat. It doesn't need to be much, just a few seconds but something to initiate a fight with and use in-between phases could go a long way to improve the usability of these specs. Here are some suggestions for each of them.
On Catalyst this could be replacing the fury from energized elements with 2 seconds of quickness and making it aoe or give catalyst a way to grant quickness when applying an aura to allies with a long cooldown or maybe give hammer some aoe quickness on one of it's air skills.
On Willbender you can change Phoenix Protocol to pulse some alacrity out when you cast Flowing Resolve. Again it doesn't need to be much, maybe 2 or 3 seconds but just enough to make the build feel more consistent.
On Mirage you could make one the traits let Chaos Storm on staff give a few seconds of alacrity.
I think these specs providing their boons in unique ways tied to being in combat is fun but you can give them more consistency without removing their gameplay identities.
Firebrand is my most played spec but Stand Your Ground doesn't need its cooldown reduced, I think the change to Hallowed Ground will be enough. Firebrand is already oppressively good as a fractal healer and this skill is a big contributer to that but even outside of playing a healer this skill feels fine at 30 seconds.
In terms of mantras it completely makes sense to have the recharge time in PvP and WvW but please please please just remove it from PvE. If I only needed to recharge Mantra of Potence every so often it'd be fine but there are times when playing heal or dps quickbrand where you might run up to four mantras at once and even though you don't need to use the last charge, because of how much damage and quickness uptime flame and potence mantra give respectively you'll always want to use the last charge with them at least, and there will be some situations where you find yourself needing to use the last charge on Solace and Liberation too. Having potentially four mantras needing to be recharged while in combat just feels awful. I know you want skills to be consistent between gamemodes but let this be an exception or if not at least reduce the recharge time in PvE to only a second or so.
Also, aside from balance feedback I wanted to say thank you to the balance team, I think for the most part you guys are doing a great job. Some of the comments in response to balance posts like these are completely vile and I hope you know that there is a silent majority that are supportive to your work and continued efforts.
To those that continue to insult and belittle the devs because you don't agree with the direction of the balance, it's not worth it. It's not an easy job and there will always be disagreements about how changes are implemented but you can be civil in your negative feedback and aside from the reason of just being a decent human being your feedback is less likely to be ignored that way too.