I think a lot of people fail to understand just how little of their total military capacity Russia is actually using in Ukraine, but this isn't because they want to but because they need to due to how thinly spread Russia is right now, in addition to invading Ukraine they are also defending the Syrian regime from being overthrown by both Syrian rebels and ISIS, AND occupying the Moldovan region of Transnistria, AND occupying the Georgian regions of South Ossetia and Abkhazia, AND guarding their border with China, AND guarding their border with NATO, AND propping up Armenia's forces, AND occupying Chechnya, etc, etc.
And this is a country that only spends 25% more on its military each year than the UK does, hence why it's going so great for them.
An issue that comes up often in this thread is that you can't just look at numbers for Russia/Ukraine and make a straight comparison, Enkore (RIP) and many others tried that back before the invasion when they were ranting about how if it kicked off the massive Russian army/air force would take Ukraine in under a week, and when myself and a couple of others dared to point out the war would go exactly as it has done we got flamed for being stupid. I legit got flamed by half a dozen people for pointing out that Ukraine would initially have more tanks than Russia in the field and on average better tanks too, because they had compared the numbers on Wikipedia and assumed Putin would send every tank in Russia. The same went for their super massive/modern air force, people were literally saying they would use their planes to take out Ukraine's SAM systems and gain air superiority (while completely ignoring the fact Ukraine had more anti-air missiles than Russia had planes to commit to the air war).
Like I said I thought the notion that Russia was somehow holding back etc.. had been knocked on the head a while ago.
I think you may be confusing the myth that they weren't sending their best units/equipment (which was debunked almost immediately). With the fact they are holding back the vast amount of them (which has been well evidenced). Roff was right, if they were sending in their best stuff on mass we would be seeing a lot more of it destroyed than we are which is why we know for a fact they are not.
You probably know this but for anyone who doesn't, here's a little secret about some of Russia's "modern" equipment: the T-90 and the Su-35 are just the T-72 and Su-27 renamed, they may have received more modernisation than the newer/refitted T-72 and Su-27 but they are still just upgraded and renamed Soviet weapons from the 70's. And before anyone says they just look similar and are based on their predecessors but they're modern designs, no, I meant it literally, the T-90 was a T-72 variant made by the USSR in the late 80's that Russia renamed in the 1990s in order to make it more appealing to perspective export customers, the Su-35 was an Su-27 variant designed by the USSR in the late 80's that Russia renamed in the 1990s in order to make it more appealing to perspective export customers. There are similar stories for most "modern" Russian weapons that are in service in any notable numbers.
Their "good stuff" isn't good at all, it's old, outdated and just has some modernisation taped on. If they were sending their "best" stuff in any noteworthy amounts, Ukraine would be destroying it in equally noteworthy amounts with the weapons we have given them. Ukraine is not, this in itself is proof that Russia is not.