The discussion seems to be coming down to answering the question: Is it good for the game that a small force that is slightly faster and has longer-range weapons can completely destroy a much larger force?
In my recent campaign update for example, a damaged Necron destroyer could potentially have wiped out the entire Expeditionary Fleet if that fleet did not have either torpedoes or fighters. However, in this case they did have both torpedoes and fighters, because I knew from previous tactical intelligence that the enemy ships were faster and had longer-ranged weapons. If I did not have those capabilities, then I would not have sent the fleet into the system in the first place.
Earlier in the campaign, I found myself in exactly that situation and lost a fleet because I couldn't get escape. In that case however, I was unprepared, had minimal tactical intelligence and was surprised by an opponent with a significant tech advantage. After that point I was extremely wary about placing my forces in a similar situation and conducted operations accordingly. I have been working on ships and technology to counter the Tyranid advantages so I can go back into combat with some chance of success.
So in general, I think if you find yourself in a bad situation in deep space against a higher tech opponent with longer-ranged weapons, you probably should be in serious trouble. However, lets look at an extreme situation. A single small ship vs a very large opposing force. Unless the tech advantage is very large, the small ship will be firing at extreme range and therefore might still struggle to overcome the shield recharge rate of the large force. Also, the large force can split up, either for most of them to escape or to attempt to surround the faster opponent.
In summary, I think there are options for a weaker, lower tech race to fight a higher tech, faster race. That is one of the challenges of the game.
Finally, having argued the above, I think there might be an option we haven't considered so far; the equivalent of 'making smoke'. Perhaps there should be some form of crude ECM that makes a ship harder to hit, but also affects its own weapons. In this situation, the lower tech force might be able to 'obscure' itself sufficiently to make it difficult for a small, higher tech force to obtain a long-range firing solution. The higher tech force would either have to move closer to gain a better firing solution, opening itself up to counter-attack if the 'smoke' is turned off, or be content with shadowing the enemy. This capability would only be useful in that type of situation and only useful for the lower tech force. My concern would how the AI handles this, but I think I could code it.