No, 125s are fine. The power level gain from having 125 vs. 150 augments this season is about 0.3 GR tiers. If you want to min-max to the extreme, sure, do 150 augs. But that’d mostly only be if you are a group player.
If you are SSF, the massive time investment to grind a full set of 150 augs is not worth it over just sticking with 125s. With the lower power level this season, it just takes way too long to grind 150 augs SSF. It’s not worth the miniscule amount of power you gain. If instead of grinding 13x gems to 150, you took all those hours and just slammed speed 90s or Visions instead, you’ll probably find a piece of gear that’s a bigger upgrade than what those augs would have given you anyway. Unless you already have 100% perfect gear and have tons of time to grind, you really shouldn’t waste the time leveling 13x augs to 150 in SSF. The power gain vs. time is just not worth it this season.
Main gems should always be roughly equal to the GR tier you are trying to push. Want to push 150? You should have your main dps gems to 150 (or at least 149 or 148).
Without the APoC from altar, I think in the vast majority of cases Comet will be better this season.
Guardian is extremely strong at low paragon. Both for damage and toughness. At 800 paragon, Guardian actually gives more damage than Aughild’s - excluding Squirt’s. The real difference with Aughild’s, as you pointed out, is it lets you have Squirt’s (or at least, both Squirt’s and CoE).
With 10 Squirt’s stacks, Aughild’s should give about 1.5-1.6x damage to non-elites, and ~2x damage to elites, but has 1/3 the toughness.
With 0 Squirt’s stacks, Aughild’s should give about 3/4 the damage to non-elites and about equal damage to elites, but still has a less than 1/2 the toughness.
So IF you can consistently maintain 10 Squirt’s stacks, Aughild’s is better.
If you are always dropping your Squirt’s stacks, than Guardian is strictly superior, both for damage and toughness.
If you are somewhere in between (sometimes have some Squirt’s stacks), it’s a bit muddier, but Guardian’s has significantly more toughness in every situation. It’s going to be pretty tough to keep your Squirt’s stacks at 800 paragon with Aughild’s. (You will be way stronger for the duration of shield pylon though).
The other thing with Guardian is that you don’t have to try and play around keeping your Squirt’s stacks. Because you don’t have it! And you have 2-3x the toughness. This means you can play way more aggressively, leverage Oculus rings better etc. So that should help make up the gap.
I think the vast vast majority of players will have better results with Guardian this season.