I personally am skeptical of the quality of most Russian troops as well, but in any case, these troops being trained in Britain don’t have to be your front line assault troops. You use them to occupy other areas of the front to free up higher quality troops for the assault. That’s the exact same logic the Russians are using when they bring on much older recruits.
The Brits are training the future trainers, like Von Steuben did at Valley Forge.
I’ve noticed the Ukrainian KIA come from all segments of their society. You have intellectuals, educated city folk and villagers. There is nothing similar on the Russian side. It’s poor ethnic minorities, mercs, prisoners, bus station drunks, etc. The male population of the occupied territories is being press gang conscripted by Russia and wiped out. I’m sure Putin considers that a bonus, too.