No, it’s not “bad”, it’s just not as insane as you claim. It won’t stop shells any more than other decently armored tanks at its BR will. Anybody with the know how is going to shred any vehicle at that BR.
Magach 5, M48A2 G A2, Sho’t Kal Gimel, Magach 6B, Magach 6R, Magach Hydra, ZTZ59D1, Olifant Mk.1, and Strv-104 all have DM23 between 8.0 and 8.7.
At 9.0, this list grows and adds Magach 6M, the Strv-103C itself, TAM, Leopard A1A1 (which should not be 9.0 in this current balance), ZTZ88A, ZTZ88B, WMA301, and the OF-40.
Note that this list ONLY contains DM23.
Vehicles within 8.0 to 9.0 with a dart greater than DM23 include the AMX-30B, AMX-30B Brenus, T-55M, PTL02, PTZ89, T-69 II G, Vickers Mk.11, Cheiftain Mk.10, T-62M-1, Object 120, and M60A3 TTS.
This list does not include any tanks above 9.0 with a limit of 10.0, which would make this list grow even further.
It is not uncommon for a dart round to frontally rip through the 103C’s UFP. You’re surviving based on if the enemy is using a stock vehicle or not at that BR.
The 103C has a horsepower-to-weight ratio of 18.4, which isn’t going to beat a Leopard or AMX-30. It’s good, but not the best.
It is shorter, but not by much. It’s a cupola-level height difference.
It’s time we stop fearmongering a tank that’s extremely conditional and not common.