ACB, we got into this a while back, and I really have no plans for getting back into repricing the official vessels as we have already done. The only vessels I'm particularly concerned with are the 'new' ones.
Personally I agree with Horizon, the Ret is appropriately priced for what it does. Over the Emperor it has more equivalent firepower, a 6+ prow armour (making it fit with the other IN vessels well) and the most important thing, Speed 20! Which means it won't slow your fleet, and it can't be Blast Markered off the board.
Fp 18@45cm>Fp12@60. I know most people would probably trade Fp12@60cm for Fp15@45cm, this is 'roughly' the break even point, so we can assume that Fp 18@45cm is about 1/5th better than Fp 12@60.
Also my impression was that the Emperor is under priced (as it is such an appealing vessel) by probably around 20 points. I think that you're suffering from the same woes, as balance is always a comparison of available choices. The Emperor's impressionable underpricing makes it appear as though the Ret is overpriced. Compare the vessel instead to the other IN battleships, and also the Chaos ones. You will find that the vessel is appropriate.
Remember that people have different views of a vessels efficacy. It is very subjective, and that is why I used a voting system for determining the points cost of these vessels. This is what won out. Additionally no one ever wants to see something get worse (save in cases of particularly broken things) so usually they would prefer everything else get better. This is almost uniformly what I did. In fact there are only two vessels which became worse in BFG:R, the Devastation (widely regarded as OP) and the Hero (which had some internal balance issues).
Around half the other vessels got better, maybe 1/4th remained the same and the last 1/4 were some sort of compromise between the semi-official HA work and my own.
I know a number of people have pushed that fleet lists be done away with and that vessels become more readily available to each fleet. I.e. the IN should be able to take all their vessels in one fleet. Now there is some merit to this, however fleet lists and limitations are designed for two purposes. Firstly and most importantly, it forces all fleets into similar limitations of relative options. Though some fleets have more vessels overall (such as the IN) they are forced to limit their options and fight as though they had comparable limitations to fleets of fewer overall vessels (such as the Necrons). Secondly these limitations are designed to add a unique character to each fleet, making a different feel and unique niche for the more common fleets, and making each opponent a unique experience. Allowing a large number of vessels prevents such situations, as generally players are good at 'feeling' for which option is the best overall, and one would rarely if ever see some of the slightly less efficacious vessels.
Simply fleet lists are comparable to the 8 dozen SM codecies for 40k, though they are really all just space marines with less difference between all the 'dexes together than the Tau are from their own auxiliary races. Since a majority of 40k players use Space Marines, this allows for them to have a more unique character amongst their numbers. Not to mention the fact that People would host massive riots if the books were merged.
And even though something was once available to a group does not necessarily mean that it should remain a part of that group. The Space Wolves once had access to Leman Russes in 40k, primarily as a novelty for the name, but the option was lost once the army was fleshed out, and the writers got their heads about them (Leman Russ goes in guard...I get it!). Think of it this way, the game would be a little less fun if every army was toting 6 Leman Russes.
I also had someone rant about 'why not remove ship classes and allow players to build their own ships for appropriate costs'. Again this has to do with the nature of players, when perfect options exist they will be the only ever taken.
