How long are the rides in moving duration? Are you on the bike pedaling for at least 4 hours for this 60 mile route?
Could you grab similar information from one of those rides to what I posted above? Duration, power (average and NP), TSS, IF, HR (if you have it)?
Basically - I’m fairly certain your FTP setting isn’t correct in whatever system is telling you that these rides are 350 TSS and it’s bothering me.
As for your sweet spot stuff…
The idea behind the base->build->specialize progression is that you periodize your training and essentially stop doing incredibly hard efforts for a while (base) so that you can build your aerobic base into a broader stronger foundation upon which you can later start doing the hard efforts (build) that you are currently doing on your outside ride in a more effective and efficient manner. This step away from high intensity work allows you to get stronger and then reach higher peaks when you do start going hard again.
If you want to seriously pursue periodized training then it is likely that you’d benefit from stepping away from the harder rides for a while and doing easier stuff like sweet spot or traditional base. But, if you want to keep having fun on your club rides then by all means do so, but remember that cycling should be fun. For you it might not matter much if you’re the strongest guy in the region if you don’t like riding your bike with your buds anymore. Or maybe you get the most enjoyment from getting stronger and being faster. You really need to figure out what motivates you before you make a decision to step away from your fun club rides to focus on your strength to that degree.
As an example, I’m a fairly competitive person who enjoys racing and trying to be as fast as I possibly can. I do a huge amount of my riding alone or indoors so that I can pursue those goals more precisely. However, I get really burned out and bored doing that exclusively so I still make sure to get out for some social rides to keep my mental focus tight when I need it to be. Everyone can tolerate different amounts of the solitude necessary for intense training - I hesitate to recommend you stop doing your club rides without knowing the impact it’d have on your enjoyment of the sport