I will preface this post by saying that I have no military experience or any particular qualifications and am thus speaking entirely out of my ass. I am not an expert or authority on any subject or topic that is written about below.
TLDR AT BOTTOM
There are those that say that the Russians are doing terribly at Mariupol. I disagree and will outline my reasons for that in this post. But first some background information. As you all know Mariupol is a city in Donetsk Oblast, Ukraine. Wikipedia states that it has an area of 244 square Kilometers or 91 square miles. With a population and population density of 431,859 (according to a census released at an unknown time in 2021) and 1,800 per square km/4,600 per square mile respectively. Wikipedia states that the battle of Mariupol began on February 24th, 2022 the first day of the invasion and has persisted for 3 weeks and 2 days for a total of 23 days. Let us compare Mariupol and the battle that is currently being conducted inside of it to other cities which have recently had battles take place inside their limits. The Ukrainians claim that as of the 14th of March 2022 150 Russians have been killed and we all know how Ukrainians love to inflate their casualty numbers.
1. The Battle of Aleppo.
The City of Aleppo, Syria is a city located in Aleppo Governate, Syria. Aleppo had a population before the war of either 2,132,100 according to the Syrian Central Bureau of Statistics (2004) and 2,301,570 by the end of 2005 according the Aleppo City Council. 2004 and 2005 are the last years from which population data is available from before the war. In 2016 the city is said to have 1,800,000 Inhabitants. The area of Aleppo is 190 km2 (70 sq mi), no data is listed for population density.
The battle of Aleppo, Syria lasted from July 19th, 2012-December 22nd, 2016. A short while after the Russian intervention into the Syrian Civil war Aleppo as encircled and a siege began which was on occasion broken. The final siege lasted from September 4th, 2016 to December 22nd a total of 118 days assuming I can do math. The combatants were the Syrian Arab Army (a solidly third world army), allied Militias and groups backed by the Russian Air Force fighting against Syrian rebel militias and various Jihadist groups. Wikipedia states that that several tens of thousands of Syrian loyalist forces were involved in the battle facing against a similar amount of opposition fighters and that there were a total 31,275 overall deaths in the ENTIRE PROVINCE of Aleppo during the course of the battle relating to the fighting. The Syrians had complete air dominance
2. The battle of Raqqa (2017)
The City of Raqqa, Syria is a city located in Raqqa Governate, Syria. Raqqa (the city proper) according to Wikipedia had a population of 220,488 while the entire area had a population of 338,773 at some unknown period before the civil war in Syria. Raqqa has a total area of 35 km2 (14 sq mi).
The 2nd battle of Raqqa as the battle is formerly known lasted from June 6th, 2017-October 17th, 2017. Wikipedia states that Raqqa was encircled on June 24th, 2017, meaning that the siege lasted 123 days. The combatants were the Syrian Democratic Forces made up of various anti-ISIS Militias well supplied with American weapons, vehicles and equipment in addition to their usual Militia weapons backed by American, French, German and British special forces and air power and ISIS. Wikipedia states that there were between 10-15,000 SDF fighters in the city proper fighting against 3-5,000 ISIS Militants. Casualties in terms of dead range from between 655-1,000 for the SDF and 1,246-1400 for ISIS. During the battle EIGHTY PERCENT OF THE CITY WAS DESTROYED.
A NATO Backed, NATO Supplied and NATO Supported Militia/NATO Troop force took several months to take a city smaller than Mariupol from a numerically and militarily inferior force and in doing so destroyed the vary vast majority of the city killing thousands upon thousands of civilians in the process. They had complete and utter air dominance during the course of the battle as well.
3. The Battle of Mosul
Mosul is a city in Nineveh Governate, Iraq. The only population figures listed by wikipedia states that as of 2021 its population was 1,683,000. Mosul has a total area of 180 km2 (70 sq mi) and no data on population density is given.
The battle of Mosul took place between October 16th, 2016 and July 20th, 2017 meaning that it lasted 277 days. Mosul was encircled on November 23rd, 2016 meaning that the siege lasted 239 days. The battle was fought between The Iraqi Army, Kurdish Militias, Iraqi Special Forces, various paramilitary forces, American, British, German, Canadian, Australian, French, Turkish and Dutch Special Forces and Air power vs ISIS. Wikipedia states that 108,500–114,000 Anti-ISIS Forces fought between 6-12,000 ISIS Fighters. I cannot be arsed to write out all the fucking casualties as you can read them in the Wikipedia article but they are significantly higher than what the inflated Ukranian Russian casualty numbers. The Iraqis and their allies had complete air dominance.
TOO LONG DID NOT READ: Russia is doing okay considering they are fighting a fairly modern, NATO Trained and supplied Military in a siege scenario with a contested airspace (in my opinion).