>How would you compare it to the Dreadnought revolution?
That strongly depends on how much new tech is shoved into the cruiser to make it a noteworthy threat.
If a navy launched a flight of SLRC capable of firing nuclear-tipped, precision guided, 1500 mile shells below the radar detection (be it the 12in SLRC or a modernized battleship caliber naval cannon - an Alaska/Stalingrad-style large cruiser is still a cruiser) which was capable of advanced first strike without being detected (the strike, not the ship), then I could see it being somewhat comparable to the Dreadnought crisis. Obviously, it wouldn't be quite a Dreadnoughting situation, since the old navy wouldn't be quite obsolete; but it would probably immediately spark a 'massive' naval arms race (for this century's scaling, it'd be nothing to the 1920s/30s) and could actually see naval treaties return.
When it comes to tanks, really, all you absolutely need to do to cause a mission kill is to poke a hole into the crew compartment. To that extent, extant 120-140mm tank cannons would defeat anything up to heavy CNT-based composites, no reason to pull out the heavy artillery and hypersonics yet.
>Strange, I thought they just need some really thick power cables. Is it because they all kind of capacitors and cooling systems and whatnot down there?
The LPU (Line Production Units) and PSUs for HELs are not individually huge, but to get appreciable power out of them you need a lot
of these combined units all working together in an array. To illustrate, to get a 30 megawatt laser, you need two thousand
LPUs, with enough leeway to allow all of those cables to get to the laser condenser at the 'turret' head. That's enough required volume to fill a Cruiser's main turret with some excess.
Incidentally, that's one of the primary reasons why the 'Lasers will bring back the Battleship' argument is actually valid. To get sufficient power to have noteworthy effect at range, you end up with absolutely massive arrays.
>And one more thing: are there combined gas/steam turbines for nuclear-powered ships? I mean that they normally run on steam, but if need to be they can switch to burning diesel with just the press of a button.
The closest to this is the Kirovs' Nuclear propulsion with Oil-fired Superheater. Nuclear cruise (~18kt), Oil flank (30kt).
With the right gearing set up, however, there is no reason why they couldn't have a dual nuclear-diesel propulsion system. I cannot for the life of me think of a legitimate reason why
they would want such a thing, but it's certainly possible.