The best seniority integration plan is NO pre-set integration plan. Every marriage will be different. Each side needs to bring its trash to the table and let Darwinism do its thing.
BTW, SWA didn't screw over Transtar. They made them an offer that was rejected because the Transtar pilots got bad advice and thought that SWA was bluffing. In the end, they got nothing but the opportunity to interview if they wanted which many did. Every ex-Transtar pilot I've come across at SWA says they should have accepted the original offer.
As far as Morris goes, yes they were stapled, but there some adjustments. Morris Captains were pay protected as FO's so they were the highest paid SWA FO's in history. Morris FO's who didn't have type ratings were given them for free, also largely unprecedented. SWA pilots voluntarily waived the scope clause so that some Morris guys flew left seat for up to a year during the transition even though they were junior to SWA FO's on the master list. Also all Morris pilots, even those previously fired by SWA, were hired.
Notwithstanding the handful who sued (and lost), or the morons who thought they would have a better future at WestPac, the SWA/Morris conjoinment was one of the cleanest, smoothest, most mutually beneficial in the history of the industry.