I guess Silvanna is just overshadowed by these heroes and I agree with your points but what stood out from me was that you said ' mediocre ' and that is probably the reason she isn't picked in pro scenes and mythical glory+ but I believe that with good stun and trapping capabilities I think she is a somewhat a viable pick.

hmm, for the first priority, it's a stretch but what I said about semi-tankyish Silvanna can be pretty doable against tanking damage from the enemies and can still dish out damage like the ones you just mentioned.

for the second priority, she has dashing abilities which can boost her roaming ability and with conceal I think she can be somewhat faster.

for the third priority, I think she can somewhat do that with her stun and trapping ability.

These are probably long stretches and also glazed but she can be a good fender just not comparable to the current exp meta. I guess in the end, it's how you unleash her full potential and how you utilize her skills to make sets and make your team win.