Yep. There's a reason all the Western navies, even the RN, invested in various types of coast defense vessels in the steam era - any ship designed for and assigned permanently to home/coast/port defense duties was going to have an inherent advantage over ocean going cruisers trying to blockade the same port.
Best,
With the obvious caveat that the whole of the attacking force can take the dispersed defenders in detail....
Consider an exercise with the US wanting to send available ironclads (not fantasy ones) to defend ports. Say in the summer of 1863 (when the Russian crisis was).
From north to south:
Penobscot Bay
Kennebec River
Portland
Portsmouth
Boston
Narrgansett Bay
Long Island Sound
NY Harbor Narrows
Delaware River
Chesapeake Bay entrance (with Baltimore and the Potomac River behind)
Port Royal, SC
With 11 major blockade points to cover the USN has exactly 11 ironclads at this point, Roanoke (which is basically going to be stuck in the Chesapeake), New Ironsides and 9x Passaics.
If the USN spreads out to try and defend everything then it defends nothing. A single monitor is easy meat for a large frigate or ship of the line. They need to be employed massed to achieve anything. Frankly the best course of action is to abandon everything except the mouth of the Chesapeake and New York, maybe detaching a single monitor as a floating battery in the Delaware.
Say you've then concentrated 5 monitors at NY and the Chesapeake. How will the RN respond? They of course have nine armoured frigates in full Commission or 1st class reserve and will soon gain another three, and have 4 ironclad batteries in good condition.*
So in summer '63 it is 11 US ironclads vs 13 RN ironclads.
The RN may be forced (if blockading) to keep a pair of ironclad frigates each off the Chesapeake, NY narrows and off Long Island sound. Thus we need to think of say 5 monitors sortieing against a pair of ironclad frigates, maybe a battery and some wooden ships.
Coming out in line ahead the monitors will come under fire from the RN battleline, say a pair of liners, a pair of frigates, a pair of ironclad frigates and the battery, plus smaller craft. The fire of 100-150 guns firing a round per minute with say a 20% hit rate. The leading monitor is basically there as a soak and will quickly be battered into an unfightable mess with the turret quickly knocked out and the deck ripped to pieces. As the others come round to unmask themselves they'll take similar fire. As they try and close the RN can essentially pull back and keep the fire on the attackers, because at none of these places is there not plenty of sea room. The monitor likely never get within effective range.
Now, if the RN is going into one of these places for an assault they'll be all up. More than one ironclad per monitor, probably leading with 3-4 batteries which were built to do exactly this. They would have 30 or 40 68 pdr 95 cwts between them again 5x 11" and 5x 15" with the 11" ineffective and the 15" unable to hit much but capable of penetrating at close range.
Of course, the RN planned immediately to tender for another nine "90 day ironclads" similar to Erebus in the event of an American war, with a budget of 60,000 pounds per ship set aside and the ships to be turned over within 90 days.
Anyway, the point being the USN faces choices, and just live with the consequences of their choices.
*Black Prince, Caledonia, Defence, Hector, Ocean, Prince Consort, Resistance, Royal Oak and Warrior. The batteries Terror, Thunderbolt, Erebus and Aetna are in good shape.