The first issue is that people are looking at Stone Armor as saying "Why isn't this more like Invulnverability?" The second issue is more generalized as people looking at ATs and saying "Why is X more like Y?" I love that Stone Armor is whacky and pro-con centric, I have a Bio Armor brute and I've basically hit a wall in that I say to myself "Why play anything besides Bio, it's better in every way." Not with Stone Armor, it's give and take.
So what's good about Stone Armor, more specifically what's good about Granite Armor? Granite Armor is every armor and aura rolled into one minus what's unique to those sets like Energy Aura's +recharge, Bio Armor's stance dancing, Invuln's +ToHit, etc. Granite Armor can only really be paired with leadership, fighting, Rooted, and Stone Skin; now here's the important part... it only /needs/ to be paired with weave, rooted, and stone skin to cap out massive mitigation even on a Brute. So what's that mean? Slots, slots, slots. My biggest weakness on my Bio Armor is a serious lack of slots and having to make sacrifices at every turn; to get my +ToHit I have to use Cross Cut and then Soul Drain to make sure I don't get misses. Granite Armor rolls all those dozens of toggles into one. How many toggles does WP have running at once... 6 or 7? Granite Armor, Rooted, and Weave (Mud Pots but that's not related to mitigation).
Yes Stone Armor has -30% damage, yes it has -60% recharge, but a Brute easily overcomes the damage debuff and you can slot to get around base recharge. Stone Armor is not designed to support dps, but you can work around it to get back to being useful with massive mitigation. I'm running a Spines/Stone Brute and have the luxury to take and slot all my AoE. Recharge doesn't even factor in because of my two PBAoE toggles and at least one AoE is always ready for use. I'm certainly not a rolling ball of death, but it's like playing a tanker that can actually do real damage.
Now, the last and key issue; getting around. The OP posted this a while ago, so not sure how Teleportation worked back in 2019 but now days it has Combat Teleport and Teleport, used together you can get around well enough. Not every map will play nicely though, toggling off rooted and granite armor can be done just eat a purple/orange in case you run into a surprise group, otherwise stay with your team and play the game how it was intended. CoH evolved over the years away from typical MMO trinity; doms, MMs, Brutes, and even scrappers can manage the alpha just fine with the right support. If you're struggling when you turn off rooted, you may not have a diverse enough team or are playing solo. If playing solo, then you're going against the grain and not playing the game as it was intended and as such will constantly run into hurdles; it's /your/ job to make your unorthodox concept work, not the devs.
Basically play Stone Armor as a delayed start tanker in teams if teleporting is too much to manage, everything will be fine, and most of the time Granite Armor's massive mitigation isn't required for most groups, mainly just on TFs and those at high levels tend to be densely packed with mobs that you won't need to drop your toggles.
Edit: I actually came up with a good solution to traveling around on a Stoner. Get stealth, and use that while darting around outside of your toggles and pop them back up when you run into a group; you get to run around with anything you please, and you won't have to struggle with face pulling. You can even slot a +Stealth enhancement into a power to save taking stealth from the Stealth pool, though honestly I skipped anything I could and anything that didn't work alongside Granite Armor so number of powers isn't an issue.
