However, these are optional levels, and such if you never level up and remain at level 50 or whatever these changes are not of your concern; also if you level up at, say, level 80, you're already super mega powerful so not upgrading your level 60 sword isn't gonna make much difference to your playstyle.
This part definitely isn't a fair statement. Look at the difference in numbers between a level 70 and level 99 sword as posted recently by
MHWilliams - that's the kind of gap you're saying doesn't make a difference to a playstyle, and you'd be seeing similar gaps across your armour as well. So a level 80 player using level 60 stuff is going to be doing maybe 70% of the damage and able to take 75% of the damage that a level 80 player using level 80 stuff, and that difference grows as the gap increases.
A small gap is easily tolerable for all playstyles, but once it starts getting above 10 levels, playing as a warrior will still be the same (just a lot more tedious), but there'll be a worse effect on hunter and assassin styles - headshots and assassinations will stop being one-hit-kills on the majority of enemies and that's the style severely compromised.
In short, if you have specific gear that you want to be useful at your level, you really need to be upgrading it before you level too far past it. Once you get too far above it you might as well just unequip it and use random epic loots because they'll work out better.
From what I can see, there's significant discussion that the new ship upgrade tier costs entirely too much.
I think the ship costs are okay (though my opinion might change if Ubisoft keep adding more). The main issue with them based on the information that was presented in this topic was that they cost huge amounts in the context of a game where basic upgrades also cost huge amounts. Now that it's clear that upgrades are still reasonably priced, the high ship costs are more acceptable, especially since a level 70 ship with all the previous upgrade tiers is hilariously overpowered anyway.
So what's the final word here? It's a bug or designed this way?
There is some change to the costs of upgrades, but nowhere near what the topic (and one screenshot within it) led people to expect. The statement in the original post that "they've massively increased the cost for upgrading gear" is flat-out incorrect.
There are new ship upgrade tiers and they are super-expensive compared to previous ship upgrades. (They are also super-effective compared to previous upgrades, and are currently unnecessary as a ship without these upgrades can still easily take on any ship in the world).
There are changes to the amount you get from selling weapons and armour to blacksmiths, but generally speaking this was a bad idea anyway, it is almost always better to dismantle these items as you get a variety of resources from this. So a bad move, economically, became a worse move.
The gold rewarded from doing some common activities was changed, in some cases increasing, in others decreasing. I don't think we have good visibility of the exact difference. The main effect will be due to the reduction in gold from contracts and naval battles - piling up as many contracts as possible is the fastest way to level up so probably a decent portion of gold earned by fast levellers is due to contract rewards. However gold has increased from conquest battles and the arena and contract missions can often push you towards doing conquest or arena battles, so this might even out.