The T-55 gets slept on a lot because its so old by now and obviously not up to modern MBT standards. I think people forget just how groundbreakingly scary this tank was when it was introduced. Even in the T-54 variant that lacked CBRN protection and stabilizers, it was a formidable weapon capable of penetrating almost every Western tank at ranges far exceeding their own and having frontal armor specifically designed to be basically immune to 88mm Pak-43 guns even at close range, which meant that the 90mm tank guns of the Patton tanks and any caliber below it was useless. It's why the 105mm gun was introduced. That's just the T-54. The T-55 CBRN defended, had gun stabilizers and so on, and this is in spite of the fact that the T-55 is a Medium tank, not an Main Battle Tank. So it punched above its weight.
Even if it is no longer capable as a front-line tank, it still retains the roles of a tank, capable of smoking any other armored vehicle frontally and even being able to penetrate a more modern tank from the side with an ambush, as Iraqi export models did to American tanks. The 100mm gun has decent HE-Frag ammunition and it's high velocity means it has good range with it. The sturdy platform also makes it excellent for being a platform for just about anything else such as autocannon mounts.
The T-55M modifications in the 70s also boosted the protection and sight-systems of these tanks, resulting in a fairly well protected artillery vehicle. They're used as secondary attack forces by both sides, such as recently at Rabotyno
To this end, despite mockery in the media, even the Ukrainians are well aware of how useful it really is. It's why they accepted the M-55S and were trying to make modernizations of the T-55 prior to the war like the T-55ABM
https://topwar.ru/241286-jeto-kruto-ukrainskij-oficer-vysoko-ocenil-primenenie-vs-rf-sovetskih-tankov-t-55.html https://topcor.ru/33720-ukrainskie-analitiki-schitajut-chto-ne-stoit-nedoocenivat-tanki-t-55.html