A large part of the risk can be mitigated by the fact that trans HRT uses bioidentical hormones and that you change the delivery route to transdermal or injections. The risk was substantial 30-40 years ago when trans HRT also used syntehtic hormones, but seemed to have leveled out to near nothing now.

Varying levels (big spikes, big valleys) are an issue too, but very few people are interested in doing anything about it. I'd love to be offered polyestradiol phosphate for instance. But such drugs are very rarely offered to anyone trans, because even after years of HRT, I could suddenly want to detransition and then this lasts too long. Or something.