Frigates are supposed to be the second smallest blue water (trans continental/open ocean fleet) ships. IDK why, but countries are making them bigger each generation to the point where they're the size of older generation cruisers, the largest non carrier type combat ships typically deployed
IDK why, but countries are making them bigger each generation
Not my area, but... I'm pretty sure there are rules and regulations on quantities of ships of certain classes in various waters - ie, one country couldn't suddenly float 500 battleships in the Mediterranean. Frigates are the second smallest ship, so if you can shove tons of strength and firepower into the class of ship with the loosest regulation, then you can essentially get more firepower into the same spaces.
Countries have been fucking with the class designations (which, from my very casual understanding, are totally silly) to circumvent restrictions for many years.
I think I saw a video on this from Battleship New Jersey.
The main time that displacements and ship sizes were actually standardised and restricted was due to the various naval treaties from about 1900 to WW2.
Before and after that (and to some degree during), sizes of each class of ship gradually crept up and up as technology advanced and everyone wanted a frigate/destroyer/cruiser/battleship that was slightly better and thus slightly bigger than what their potential opponents had. Scope creep.
Prior to WW2, this simply meant that the biggest ships kept getting bigger and bigger, and then other classes were 1/2/3 sizes smaller.
Post-WW2, while each class kept getting bigger and more expensive, the advent of air as a serious threat meant that the largest ship class just disappeared - the US hung on to battleships for a while for specific applications, but never built new ones. Too expensive, too many eggs in one basket, and not enough actual need. No-one expects to have another big naval slugfest; radar, aircraft, and missiles have obsoleted large naval guns and armour.
Each successive 'large gunboat' class has disappeared somewhat later, as it reaches the point where politicians and admirals decide we can't risk losing this many people and this much cash in one hit.
Aircraft carriers have stuck around because they're very useful and they're not intended to go within range of enemy heavy weapons, but a battleship with 16" guns and armour to suit is very overkill and expensive for anything but fighting another battleship. Shore bombardment is about the only role they could have left, and much smaller ships do that just fine.
Aircraft carriers are staying because they're force projection plate-forme. Like they're not meant to fight, rather they are forward bases that you can move on the water. And the navy is meant to protect them.
I don't think there are any real rules like that. This whole meme is just like boomers saying back then everything was better and the right way to do things.
In non UK Europe most combat ships are frigates. We don't use the destroyer or cruiser categories. This is different in the US and UK navies apparently.
From Wikipedia : only the US and Russian navies have cruisers nowadays.