Hi @basdenhoed and thanks for tagging, @danmoyle,
Correct, this is currently expected behavior. It’s not possible to show marketing email sends on objects other than the contact object.
A workaround here would be sending a one-email sequence instead of a marketing email. This email should then show up on all records. However, this requires a Sales or Service Hub Enterprise subscription: Enroll and unenroll contacts in sequences using workflows
One reason why this issue arises in the first place is how you’re currently using deals and pipelines. @franksteiner79 has written a great summary of how contacts, deals, and pipelines should ideally be used: https://community.hubspot.com/t5/Ask-Me-Anything-and-Panel/AMA-Demystifying-HubSpot-s-lifecyle-stages-deal-stages-and-lead/m-p/514256
tl;dr: It’s not recommended to use pipelines for lead management but only for opportunity management. For MQLs and SQLs deals should not be created yet. These should still be contacts and if that was the case, you could see those marketing emails directly on the contact records.
I understand that this might be a big change to how you’re currently working but it is also the 1 mistake I see when companies start using the HubSpot sales tools. It’s going to complicate reporting in the future and make some use cases harder, require additional steps and require more effort.
If you stick to your current method, keep in mind that moving deals between pipelines will also break many default deal reports.
Hope this helps!