Some season effect, well ok but that is to do with peoples behavior patterns rather than a seasonal change to the virus transmission itself - is that enough to mitigate for lifting restrictions and taking the risk on an 'if' people do x. Irish summers are a mixed bag so no absolutes on all time spent outdoors. So there was little drop in cases/deaths in the northern Summer period - theres your argument that there is only a 'modest decrease' in covid cases in summer time no? Differences in samples from different times of the year will currently show trends heavily influenced by restrictions and total lockdown eg a drop in cases from May to October seen here. It would take a number of years to extrapolate real trends from season to season. There was one virologist's prediction last Spring and he seems to have been on the ball most (wish I could remember the name) - that we will continuously go through peaks and troughs as we lockdown and then ease restrictions and end up in lockdown again (or circuit breakers as 'lockdown' was being named) etc. until there is a vaccine (at that time there was none) or we achieved a zero covid island and closed borders. So while the cycle may have aligned seasonally over the last 12-16months it wont necessarily continue in that manner, while there may some seasonal deviation for the reasons you mention.
Here is a similar graph of ICU cases(and projections) from the UK but same idea if it were in the cycle of restrictions/ease restrictions = covid decrease/increase.
https://assets.weforum.org/editor/xM...-l78jhgnt4.JPG
I dont see how we could reasonably risk the suppression of cases by holding even 25% capacity crowds in the Aviva until the breaking of the above cycle is very likely, so vaccination of 75% of the population and really really hope that there isnt a vaccine resistant variant from Brazil/India or anywhere where there is a significant outbreak or we could be back to step 1. There are a number of confirmed cases of the India variant in the UK and it is a given that that number will rise after the large scale close proximity gatherings across England recently. Crazy stuff when 75% has not been achieved with 1st jab never mind 2nd. Political Russian Roulette and hoping to surf the wave of early vaccination momentum. Seeing how Scotland with a lot lower incidence rate, similar vaccination status, yet are only considering lifting some restrictions yet. We are far off the levels of vaccination to be able to agree to UEFA's demands on hosting Euro2020 games and the govt made the right call in the current circumstances!