I think your trepidations about shore diving in big swell is absolutely valid. I've seen some really bad accidents when spearos get worked in the surf zone - putting sharp objects and humans together in a spin cycle are bound to cause some injuries and lost kit.
In saying that, although I've a had a few close calls, I think it's possible to get out and back without too much risk.
Going out in a running swell is all about timing and finding the correct spot to enter. What I do is when arriving at a area, even before kitting up, is take some time to sit check out the area and try to find the best entry spots and also a pattern to the swell.
Look for sheltered bays, gullies, rip currents and eddies. Sometimes difficult to spot in a beach break scenario but they are there and walking up and down the beach and studying the surroundings can reveal these areas. If used correctly a rip current can get you out beyond the surf zone with minimal energy expenditure. However, trying to come back in the same rip can get you suck in the surf impact zone and make exiting virtually impossible, so use the natural features to your advantage.
Time the lulls in the swell. When surfing, if I get to the backline without getting my hair wet I know I timed it well and took the correct path out as I didn't have to duck-dive any waves. I try and do the same type of thing when diving. Count the sets and get an idea of how many waves in a set and which waves in the set are the biggest. This will give you and idea of when to enter the water and go for it. Look at where the waves peak and break and plan a path around the heavy impact areas. When duck-diving a wave try and go as deep and close to the bottom as possible, the closer to the bottom the less turbulent the water.
When coming out, again, get your timing right - wait for a lull in the swell. Look for the area on the beach you identified as a good spot to exit and assess if it still is. Conditions change and an area which looked good before may now be hazardous after a long dive. Once you've made up your mind to go out and you do get caught in a big set turn around, face the waves and duck-dive the waves until you see a long enough lull in order to continue then turn and make your way back. If you do get nailed by a big wave the best thing is to relax and go with the flow, trying to fight it will just waste energy. Try and stay as relaxed as possible in the surf zone. For sure there are some rare occasions when one is required to sprint but in general keep the heart rate down, pushing your body into the red will make recuperation to deal with another set very difficult.
A buddy of mine got impaled while kitting on the shore and wave pushed him onto his spear gun. So when entering and exiting keep track of your spear point and make sure its pointing a safe direction. Also if you find yourself in a sticky situation there is no shame in discarding kit in favour of staying safe. I consider all my kit as consumables and have no problem leaving a gun behind or dropping a weight belt.
I know it can be hard to take a half an hour to chill when you can see your planned dive area is looking epic with birds working and bait fish busting the surface but getting a feel for what's happing will not just give a better idea of how to navigate the surf zone but also put you mind at ease making the whole dive more relaxed.
Lastly, listen to your inner voice, if there is something telling you that it just doesn't look safe to enter, don't. Come back another day when things are looking better.