budget diy tube preamp beating many expensive preamps... problem with my system?

Try buying decent cables,the Wireworld Eclipse is a excellent cable

snd is built better then most  at 2x its cost.and better parts quality.

I’m sure my heavily modded phono preamp sounds better than many models three times the price. The price doesn't guarantee sound quality.

Don’t underestimate a DIY amp, properly designed and built.

Especially Bottlehead.

Not paying for the distribution network, a fancy box, or the labor to assemble it.

it can be because of some system matching issues.

You also do not explain where there are sonic difference that you prefer compared to the other units.

So a happy accident. You found after trying several other more expensive preamps that a simpler and less expensive DIY preamp brought out better sound. Enjoy your good fortune.