Some models have strong low notes, some have easy high notes. We probably can’t have both. That said, I wouldn’t call the lowest notes on my Yamahas ‘weak’. My 300 series alto has a poor B natural, but the lower notes are fine, perhaps a little quiet, although still full and warm. But ‘the higher the pitch the louder the dynamic’ is basic physics for a recorder. I get the most out of the low notes by breathing warm, slow air (think dahhhh, rather than doooo) and maintaining breath support.
Descant and treble recorders.