It absolutely isn’t “decidedly worse” than the T25. It’s far more mobile and with the added stabilizer and faster reload I would much rather play the T20 at any BR compared to the T25.
Both KwK 40 variants (L/43 and L/48) are worse in every way except reload, which is identical. The L/48 gets closer due to it’s longer barrel, but still fires a slower projectile, with less penetration, and with less damage.
The armor on Pz.IVs is poor, even on the Pz.IV H with add-on track armor because the majority of the turret is still just 50 + 15 mm effective. The mobility of the Pz.IV H is also not that great because it’s the heaviest Pz.IV. Overall the M4A1 (76) absolutely has better armor (due to turret, hull is similarly effective on both tanks), better mobility, and far better firepower as not only is the 76 mm better, even if only slightly, it also has a .50 cal and a stabilizer.
It’s a great gun but the M36B2 is more a sidegrade to the M36 than anything. It makes a massive sacrifice in mobility in order to have HEAT. Both could and probably should be 5.7.
17 pounder has great penetration but nowhere near the same amount of damage since it is solid AP.
Since you compared the Fireflies to the M4A3 (76) you should also mention how they have poor gun depression (only -5°) and nowhere near the same amount of mobility, on top of slower reload (keep in mind they only have 5 ready rounds). Also I certainly hope you aren’t including the Comet in there with the 77 mm gun.
The M4A1 FL10 seems like a great vehicle, but the M4A4 SA50 has a much longer reload, 9.75 to 7.5 seconds depending on crew, and has much worse mobility, due to the 4 ton higher weight.
The ARL-44 only has good armor specifically on the upper glacis, everywhere else is mediocre at best, the mobility is also mediocre, and the reload is 10 to 13 seconds, which isn’t exactly “decent fast-firing”.
Firepower is undoubtedly worse. Similar penetration values, similar damage, but the SU-100 has a 40% longer reload than the Jagdpanther. A Jagdpanther with a completely stock loader will reload faster than an SU-100 with a completely maxed out loader (9.75 seconds compared to 10.52 seconds).
The armor also isn’t “slightly lower”. The SU-100 upper glacis gets penetrated by something like the US 90 mm with M82, and the lower glacis is unchanged from the T-34, still 45 mm at 60°, and while the Jagdpanther’s lower glacis isn’t anything phenomenal (currently 55 mm at 55°), it does have the transmission behind it.