You haven't factored in an expected cost for when Jet2 *(insert airline here) trash your best bike or mangle the mech hanger etc. nor the cost of bike travel box / bag
I have. Hire of bike box around £60 a week I think. Cost of extra luggage again about £60 depends upon airline. Might be a transfer cost at other end so let's say £150 all in to take own bike. A Di2 equipped hire bike is around £40 a day but if have for a week would probably be about £35/day.
So yeah, so although overall roughly similar cost wise probably not worth hassle for a week. However if you go for 10-14 days then it is worth it.
Obviously if you already have own bike box then cost less.
Other factors are some want to take own bike as it's got perfect set up for them also availability of bike at destination. If you happen to go over to Mallorca when say 312 is on then chances of getting bike are greatly reduced.
As for damage, yes that can happen but in a good bike box less likely. For decades I've flown abroad surfing and only once have I had a board damaged. Surfboard bags are way less protective than a hard bike box.