The marriage Yoshimoto forced on his niece Tsukiyama with Ieyasu can be interpreted as a measure to tie Ieyasu to the Imagawa family, but it can be also understood as an honest special favor to turn Ieyasu into a relative of the Imagawa family.
姪である築山殿を嫁がせたことも、家康を今川家に縛り付けたという解釈もできるが、順当に考えれば今川家と縁戚関係を結ぶ事であり厚遇と言える。