The issue with the Challenger 2s is three-fold
Mobility is one of the CR2s weakest traits IRL, but it has a number of issues that serverly affect its handling. Trying to turn in the CR2 is like slamming on the handbrake (this might be finally being fixed at least partially) but has a number of related issues, like its acceleration being too low.
Survivability. Challenger 2 is one of the most heavily armoured tanks IRL, but in game, it is missing a LOT of its protection. Most of the bug reports are related to its protection. Its hard to get data for it that isnt classified, so that causes issues. Where data is lacking, the devs seem to prefer under-performance than over performance.
Fire-power. This is tricky. but the really big bit is that L27A1 shells on the CR2 (and other shells like DM53) are designed to perforate ERA plates on soviet tanks. That feature is currently missing. Meaning L27A1 has one of the lowest pens of all NATO tanks. On top of potential general underperformacne as well. Fire rates are also a balancing decision, with CR2 apparently able to acheive up to a 3 second fire rate, but in game its about 6.
You can read up on the bug reports here:
Then the general ground tree is lacking. With them choosing to give us more MBTs rather than any light tanks or IFVs for top tier. We now have 6 MBTs, 1 Premium MBT and 1 ATGM launcher and thats it for top tier. This leaves us strong is some areas, but completely unable to adapt to situations. ADATS is our SPAA system but its classed as an ATGM launcher in game and therefore does not benefit from the reduced SP costs of SPAA.
Stormer HVM currently doesnt work, the Starstreaks phase straight through air targets quite often.
In air the situation looks fine on paper, but the biggest issue is the lack of additions. Harrier Gr7 and Tornado Gr1 are “fine” but the Gr1 is missing loads of features and is underperforming quite badly at the moment. Tornado F3 at 11.3 being added after 12 was just insulting and its totally DOA in an uptier, but perfectly usable if you are against 11.3s or below.
we are only now getting a 12+ aircraft this coming major update, but its from South Africa not Britain in the form of the Gripen C. which is a great aircraft, but its a bit of a shame. But thats it for the entire year. The Tornado F3 and the Gripen C, 9 months apart
SRAAM and Red Tops, 2 unique briitsh A2A missiles are really buggy at the moment, and just dont work anywhere near as well as they should be.
In Naval, our top tier Battleships are 15 inch guns, and to balance them, they have a massive increase in shell dispersal, which really badly nerfs them.
I cant comment massively below top tier much these days, ive not played lower tiers in years, but APDS and solid shot always underperforms and is really hard to use. We have some really great vehicles, but they are unfrotuantely few and far between and most could be great, just they are missing… something.
This video really does sum it up quite well:
Spoiler
https://www.youtube.com/watch?v=XBX1SKSmdN4&t=1s