What you're saying is absolutely not true. I'll put short version to make it easier to understand (and that's aimed at me, I seem to lose the point the more I write)
1) Shield Cell need a while to kick in. It's not a long time, but enough to have the shields taken down, rendering SC useless for the time being. Happened to me quite a few times when fighting pirate NPCs and I payed with my life few times. Press-to-win?
2) Sure, they can tip the balance towards player using them. That's not why I believe they were intended. How about taking on stronger NPC oponents that you normally didn't stand a chance of defeating? How about taking on multiple NPC opponents? How about escaping that damn pirate NPC in your Hauler? How about repelling multiple NPC fighter-class opponents in your frigate-type ship? How about surviving in war zones?
3) What you seem to deliberately skip is you also have a limited supply of shield cells. Once you use them all, that's it. Why not mention that?
Considering all of above, I do not feel shield cells are overpowered. They give an advantage but please tell me - compared to the rest of NPC engagements in the game - how many times did you fight equally-skilled player where shield cells tipped the balance? I haven't once. On the contrary, it saved my skin a lot of times when I had to fight stronger NPCs. They were Dangerous Cobras, I was Mostly Harmless Eagle. That is what I call balance, so your smaller, inferior armor-wise ship still stands a chance.
Oh, and I had a fight against 'conda (not even elite) and I was blown out of the sky very quickly. Maybe more skilled player could make short work of her in Eagle, I certainly couldn't. But the whole "mount-SC-auto-win" theory is as far from true as it can be. Not without looking into full range of situations it can be used in - judging its OP-ness by just one scenario is wrong and leads to false conclusions.
I think it is, opinions eh?
The only scenario I'm judging them by is combat, whether it's 1v1 or 1v many or 1v a much bigger, more powerful ship they have an overpowered effect.
My take on your points:
1. That's practice and timing. After a while you get a sense of when to trigger them so that your shields never drop.
As long as you're able to get on the conda's tail it's possible in an Eagle to not lose shields at all using cells, I've done it recently to prove the point. I could not take down a conda, or it would take a LOT longer, without the cells. Anything smaller than a conda and they do trivialise the encounter for me. I've made a choice not to use them as a result.
2. I'm not sure I agree about the intended use, but regardless taking on stronger npc opponents is possible with skill, ship upgrades and clever energy management as it stands. Shield cells skew it far too heavily in the player's favour.
3. Yes they are limited, but resupplies are never far away and if you're doing assassination missions you only need them for one encounter. Also, did you know a Cobra can currently carry as many as 49 cells? An Eagle 20+?
how many times did you fight equally-skilled player where shield cells tipped the balance?
Every single time I've had a pvp encounter unless my skill level was much, much higher.
When they were introduced I had to run from pvp encounters where I was the better pilot because they had cells and I didn't. So I got them and encounters then became about cell management and whomever has more or uses them more efficiently gets the upper hand.
I've been flying since the premium beta so I have a lot of flight time, and I'm quite comfortable taking on elite Cobras in my Eagle. I'm not saying that to show off, just to point out the result of time acquired skill vs. using shield cells.
I do hear what you're saying about how helpful you find them but there are other ways that aren't push button. For example, did you know that 4 pips in systems more than doubles the damage your shields can take? (3 pips increases them a bit, maybe 10-15%, 2, 1 and 0 do virtually nothing.) Use that when you're under fire to give you time to get on their tail.