Frost can't go afk in any content where you actually need him rather than use him to be extra lazy. Gotta be casting globe every four seconds in high level content because even the absorbed health from level 100+ enemies won't keep it up long.
I think that just depends on how you build your Frost, a maxed out power/eff build (with stretch for usability) has around 500,000 HP worth of bubble in one use of an energy pizza. My bad frost build has around half that, and that's enough to sit around and let twenty level 100 bombard eximus units fire at me for a few minutes without much worry. I think Fleeting Expertise is the real difference between having a virtually indestructible bubble and one that requires constant recasting.
That sounds off. My rough calcs by memory make the max eff+power+armor build out to around 800k HP from a full large energy pizza if you're not wasting anything.
Of course that's not a realistic build. You need range for the bubble to not be shit. You need Corrosive Projection at that level of play rather than Growing Power. Relying on pizza spam to keep your energy up rather than running Primed Flow and spamming kiddo mode energy regen is more vulnerable to getting caught without the energy to recast when needed. You also miss out on Chilling Globe, which is IMO an absolutely vital part of his kit for high level play, since it's a coinflip for not getting gibbed if something slips through. Most importantly, it's less efficient than casting every four seconds.
The really important thing to remember is that if you're pressing 3 every time the invulnerability is about to be up, you're stacking globe health far more efficiently. It's invulnerable for 4 seconds no matter how much you spam the ability, and globe health is irrelevant when it's invulnerable. It's much more important to have a good bubble size and Chilling Globe just in case, especially for high level content. A single Lv100 Corrupted Bombard can put out ~11k damage per shot. A Lv155 one can do 25k per shot. A Lv.155 Corrupted Heavy Gunner can output over 11k DPS and will continue to do so until it dies or is CCed. A Lv.100 one will still do a respectable 5.6k DPS.
In a large mob of Lv100+ enemies, six digit globe health will melt like butter in the sun. You'll need to recast so often that it would be more efficient and less prone to failure to just recast every 4 seconds instead of spamming it and trying to catch it before the health pool goes down.
Of course this is all predicated on playing Frost in something equivalent to T4D. These days there's no actual challenge in the game, and certainly no objective-based missions difficult enough to require Frost or a similar frame to be played in a hyperefficient manner. You can basically run whatever you like in anything and do okay if you know how to play the game and aren't running a full loadout of unleveled gear with no taters or forma.