Note that in all of your examples pilots are moving UP a category.

We have 5,000 retirements in the next 10 years and 10,000 in the next 20. There WILL be upward movement as long as we don't shrink so there must be a mechanism for pilots to use their seniority to move UP the ranks. Every retirement will naturally trigger several training events as pilots shuffle up the ladder. This is one of the major reasons why the company wants and loves "categories" instead of totally individual fleets. For example, when LUAL placed the 747-400 and 777 in the same pay band it was considered a concession with a dollar value assigned.

Meanwhile, there are already existing freezes in the contract for pilots that don't move up a category but still bid for something that causes a training event.

For historical comparison, CAL used to do a twice yearly system bid free-for-all that could trigger massive training requirements (or not, depending) while UAL once upon a time had training freezes so onerous that new hires(!) were able to bid 747-400 FO because all the pilots senior to them were already in seat locks during a period of rapid movement.

Thus, we already have a pretty good "balance" in the UPA, IMHO, and I would oppose any effort to further restrict pilot movement. If the company wants to save training $$$, better management and planning is the answer.