The following reasoning isn’t effecting any gameplay at all from how Colossus plays currently.
Right now as it stands, Colossus always wants to hit MS on cooldown in the execute phase with 2x execute debuffs and 1x overpower buff, it’s not exactly opting to never press MS in favour of execute at all since it’s got 3 GCDs inbetween each MS cast anyhow.
There was always a reason to press MS over anything else in this window on cooldown. This negatively effects the Demolish CDR too, since executes during the execute phase accelerated it’s CDR with having an additional 2 demolish stacks added inbetween every MS, while also making sudden death procs less impactful as they provided an additional stack when they procced outside of the execute phase which was a nice synergy.
Even when talenting into Battlelord, you still opt to hit MS over Execute as it stands right now when the proc resets.
This is overall a net negative gameplay change as it lowers the frequency of Demolish CDR in execute which felt great in it having a much larger reduced cooldown during the execute phase so losing more frequent Demolish casts just feels bad.