I wanted to unlock the Guardian fighters. So, let's see what that requires and please tell me this isn't "grindy":
1) go to a guardian nav beacon and charge it up; repeat the process 3 times to get 3 keys (this one's actually pleasant, as it requires no instance resetting and is fairly short and nice to look at)
2) go to a guardian site; charge beacons, use the key, get 1 fighter blueprint; repeat process 3 times (requires instance resetting, getting the first blueprint is fun, but the fun evaporates really quick when you're doing the lengthy process a second and then a third time)
3) realize that you also need a bunch of guardian materials; start repeating the process above (albeit a simpler variation of it) to get these mats; you need a LOT
4) realize that you're missing a lot of Guardian epsilon data packages; get them by either repeating the process above forever or go to a specific location where 2 data pylons are next to each other: scan both, relog, repeat as many times as needed (pure RNG if you get the data you need).
If you limit yourself to one ruin / game session so as to not abuse instance resetting, then the above process would take a VERY long time indeed.
All of the above is a bit out of the bubble, so to even start the process you need to jump something like 12-15 jumps in a decent long-range ship (much more if you don't have one). And if you miscalculate and don't have enough mats once you get back, you're going to have to repeat parts of the process above. Of course one doesn't need to unlock all 3 fighters at once, but due to the time wasted travelling to and from the Guardian sites... well, most people will likely want to get this over with.
My next goal is to unlock the Federal Corvette... and while I was able to get the FAS with very little grind (i.e. by organically playing the game), the process of reaching the Corvette is a bit crazy... same deal with the Cutter (which I already have - so I know what I'm talking about).
If a goal one undertakes is even a little bit larger, then the grindy aspects of the game rear their ugly head extremely quickly. Now, some "grindy" aspects are... relatively OK (like getting mats for engineering upgrades is OKish); while others just make me wonder "what the hell were they thinking when they designed this?!" (like unlocking certain engineers themselves which requires mindless flying back and forth transporting cargo or the above mentioned gathering of epsilon data packages).
I do see where you're coming from, but its worth remembering that those large goals are an accumulation of little ones. Lets just take the two biggest ones you mentioned, unlock guardian fighters and get a corvette.
I'm in the mood to crank out some credits. So I do. I'm also aware that ranking up for a 'vette is on my to-do list so fed missions that suit my current goal of earning some efficient cash also happen. In pretty short order they'll be good ones too, even if I'm new to the area, since profitable trading turns stations green pretty quickly. Maybe take a break in the middle of a session if a rank-up mission pops, maybe not. I'm not wasting any fed rep I gather anyway...
Maybe I'm close to a rankup when I start a session and decide to spend this one specifically running fed missions to get it to tick over...
If I feel like shooting stuff there's always bounty hunting in fed space or finding a nice spot where two fed factions are squabbling so that whichever side I tun in c-bonds for I still get superpower rep out of it... It all fits in with all the other little goals until I decide I'm in the mood for a honking cruise...
On that play session, since the guardian gear is also on my wishlist, it will be in that direction. While I'm traveling, though, the fact that I'm heading to a guardian site is incidental, I'm primarily focused on getting eye candy for my desktop wallpaper and interesting astro data. Once outside the bubble taking it easy(-ish) still plotting fast routes but not using jet cones, for example. Even on well-traveled routes you still pick up a few first discoveries that way. Obviously this is one of the few sessions where I know what I'll be doing in the next one...
Hey, I'm in guardian space

let's hit a few sites, run the puzzles a few times trying for better times - think of it as a buckyball obstacle course

of course since I'm not daft and I know a lot of guardian mats will be needed there's no way I won't pillage every last scrap out of each site between runs before I reset the instance. Since I'm out here anyway I may as well hit more than one site, even though the fighter blueprints I particularly want are only in one place that I know about... I'm probably going to want to bug the tech broker about other stuff too in the future, after all. So only run each site a few times, not enough for it to get silly. Maybe for variety slowboat on an efficient route between sites while doing some more serious honking. But all too soon it's time to think about doing something else, which means heading back in.
On the run back in I'm still honking stuff but this time I am using jetcones. My goal here is to sell all that explo data at a fed station. I still want that rep in addition to the credits and he exploration rank, after all...
A few play sessions later, during which one of these smaller but varied goals gets achieved in each, there's the mission for rear admiral, and Glory Be! I seem to have enough credits accumulated that even after paying for my new 'vette I've got more in the bank than I had when I decided that I'd quite like one. I think I'll put a guardian fighter in its bay, and while I'm at it this IS a 'vette after all.. did I collect enough stuff while I was out there to bolt an FSD booster onto its lazy behind?