I’m going to be really blunt here, hopefully it doesn’t get taken the wrong way.
At 93 kg, you’re going to be at a big disadvantage when the road goes up with a relatively low FTP of 300W. Emphasis on relatively, because it’s in comparison to the other rides in the group. On a flat or downhill, your weight doesn’t make much difference, but on a climb, 3.22 W/kg will spit you right off the back in a fast group. On the flats, work on being as aero as possible to make the most of your power. Don’t be a hero when you pull, it’s possible you feel like you have something to prove, and are cooking your legs before the fun really starts. Since you’re on the bigger side, if you’re sitting too upright, wearing a loose-fitting jersey, riding on the tops when you’re pulling, etc, you’re going to be wasting most of your power on drag rather than speed, like how an incandescent bulb produces more heat than light, compared to an LED bulb.
There’s a difference between doing 300W for 20min when you’re fresh, and doing the same once you have 50-100km in your legs. Intervals are all well and good, but if that’s all you do, you build a brittle engine that’s only good for short rides, in my opinion. Several 90min Z2 rides during the week, and a good, honest 3-5 hour Z2 ride on the weekend will do wonders. I’ll also add that it’s hard to do a good Z2 ride with a group, at least in my limited experience. Pick a reasonably flat route so you minimize the time you’re not pedaling because of a descent. Holding a constant 180-210W for several hours might sound easy, but you’ll feel it at the end, if you did it right.
You said the people in your group have been riding for years, which means they’ve likely had lots of Z2 time, and have built up strong aerobic engines. That’s also why they’re surprised by your interval intensity compared to what they’re doing. Unless you’re ridiculously genetically gifted, you’re not going to cheat the system, and build up in 2-3 years what they’ve had 5, 10, 20+ years to build. This is what also helps durability/sustainability, or being able to put in a hard effort on a climb, and properly recover for the next effort, over and over.
Just for my N=1 sample set - turning 40 in July, 78-79kg, 177cm, 81cm inseam, 335 FTP. Over the past 1.5 years, I did lots of SS and threshold with TR, but I almost always had a longer Z2 ride on the weekend. For the past 3-4 months, I switched to doing a lot more Z2 instead of SS, since I was averaging 10-12 hours per week, which (I think) is enough for a more polarized approach. So far it’s been terrific. Twice a week I’ll do a harder ride with VO2, threshold, or SS. When I do the latter two though, it’s typically for longer durations. Threshold and over/under intervals are 15-30 minutes, SS (88-92%) 30-120 minutes. When I was doing tons of SS, I usually felt good, only a few weeks here and there where the fatigue started to creep in, and I’d get irritable. That’s improved in the past few months, too.
Anyway, I’m rambling. Be more aero and efficient on the flats. Build a bigger engine with long Z2 rides (at 12 hrs/week, you have the time). Reducing intensity will also leave you fresher for the group ride. Not sure what your body composition looks like, if you have some weight to lose, focus on that, count calories, no late night snacks, just water, i.e. no/minimal calories, for rides under an hour, etc.