Robertson is doing fine, he just doesn't really have that much top 6 upside and has limitations. His line is also limited because him and Domi are relatively small players so when on the same line .. they don't do well in certain match ups.
I would look to package him in a deal this year or next year. Not because I think he is a bad player, just because he will probably become expendable after next year. The Leafs have too many almost ready wingers, who have higher ceilings. By 2025-2026, he won't be among the top 9 wings on the team.
2025-2026 Wingers
RW: Marner, Nylander, Jarnkrok
LW: Knies, Cowan, Grebenkin
Where does Robertson fit? This is similar to the Kapanen/Johnsson years. At some point you have to move them and not hold on too long.
If the right deal is available this year for a top 4 D, you have to consider including him. Plus, I think Steeves can slot in him on the 3rd line without too much trouble. If not, you can also give McMann and Abruzzese opportunities. If you sell high on Robertson, you can then try to up Steeves' value this year and next... before all the wingers in the pipeline arrive.
The only reason I may keep Robertson until next year is because he may be still viewed as injury prone.
So if he completes this season without a problem and puts up 40 points, he is probably seen in a better light next summer/year in a trade.