I basically agree with the first part (I said a dedicated combat vessel should have more punch than a trade ship) but it shouldn't be like ten times more shields.
There are three sources of shields in the game:
- main shield generator
- shield boosters
- shield cell banks
The first costs one internal which - unless you were planning to take advantage of the complete uselessness of NPCs by evading every interdiction, low-waking from the ones you can't evade, and high-waking from the ones which masslock you - should be one of the larger ones even on a trade ship (I use one of the sixes on my trade/exploration Python for the shields)
Using the second for shield boosters is very common on trade ships already, doesn't compromise trade ability - and trade ships can carry at least as many of them.
The third, I agree, is really for combat ships only (though if FDev make NPCs more dangerous I'll happily swap another 6 on my Python for a bank)
Both traders and PvPers can apply the same engineering to their ships. FDev have made all the shield engineers ones who can be accessed almost entirely without any combat at all (absolute pacifist characters will be limited to grade 3 shield boosters):
Farseer - direct non-combat unlock, SB 1 (also has G1 powerplant, which is enough to get 15-20% extra power from overcharged and a good secondary, and G3 drives for running away better)
Martuuk - direct non-combat unlock, SG 3
Chung - non-combat unlock, after Dweller who is also non-combat - SG5, SB3
Vatermann - non-combat unlock, after Jean who is also non-combat (and provides extra armour), after McQuinn who does require a small amount of combat - SG3, SB5
I'm assuming for the following calculations the "extreme" settings on Coriolis. Shield boosters and generators both have nice secondaries so getting blueprints to go beyond that is fairly easy but doesn't change the general pattern.
That's certainly enough to make a trade ship which can run away from a PvP fit ship. A Python with a 6A shield (thermal 4 or 5), and 4 shield boosters (2xresist 5, 2xheavy 5) will have ~1000 MJ base shield, or with 4 pips to systems and counting resistances, ~4500 MJ of effective shield. Sure, the same Python fit for PvP might have a prismatic, a pair of SCBs, and some extra secondary effects (but one of the boosters swapped for a heat sink) giving it over 20000 MJ of effective shield [1] ... but 4500 is certainly still enough to run away effectively.
(A shieldtank FDL fitted for PvP would only have around 7500 MJ of effective shields, is probably more common to meet than the Python, and is likely to be faster - but the trade Python can low-wake from that...)
[1] Until someone uses feedback cascade on it, anyway.