Product Owner and the Development Team collaborate
The Scrum Guide is very clear on these aspects:
- Product Owner and the Development Team collaborate on Backlog refinement:
Product Backlog refinement is the act of adding detail, estimates, and order to items in the Product Backlog. This is an ongoing process in which the Product Owner and the Development Team collaborate on the details of Product Backlog items.
- Product Owner's decision is final on prioritizationordering the items. However, dev team gets an opportunity to present their point of view.
Product Backlog management includes... Ordering the items in the Product Backlog to best achieve goals and missions; ...those wanting to change a Product Backlog item’s priority must address the Product Owner.
- Dev team's decision is final on estimate. However, Product Owner gets an opportunity to present their point of view.
The Development Team is responsible for all estimates. The Product Owner may influence the Development Team by helping it understand and select trade-offs, but the people who will perform the work make the final estimate.
However, the Scrum Guide is silent on technical debt. There is no mention of technical debt or anything remotely like it in the Scrum Guide. When the dev team strongly feels that a technical debt needs to be prioritized, otherwise there will be bigger problems down the road ("A stitch in time saves nine"), they are powerless to get that prioritized. If the PO refuses to give enough attention to the views of the dev team on this aspect, I advise my dev teams to include the technical debt in their estimation of related features.
So the answer to your question:
Do you consider a Tech Lead (or any other qualified developer) should be part of this prioritization process...
is YES, you have a right to participate. The Scrum Guide says so.