SPG and Link are really two very different REITs, operating in two very different markets.
SPG owns large malls in the US. Link owns predominantly small malls, wetmarkets, and car parks in HK, plus a couple of large malls in Australia and China.
So, the sector they are operating in is different, as is the country. In the US there is a mall apocalypse, and for this reason SPG has been dropping a lot over the last years (-76% since 2016). According to most analysts (e.g. Brad Thomas) the drop in the price of SPG isn't really justified, because they have the best malls in the best locations. The malls that are closing are mainly in the suburbs, in the middle of nowhere, where people need to drive 30 minutes. This is not the case for SPG's malls. SPG also makes a lot of profits and has huge reserves to invest in modernise their malls. The argument is that one way or another, malls located in good places will always exist, as long as they reinvent themselves to satisfy shifting demand (e.g. some shops can even be transformed into offices). The payout ratio of SPG is only 82%.
As you know, most of the business of Link is located in Hong Kong, and HK has a few differences with the US. Mainly: 1) The weather is rubbish, so when people go out, they spend their weekends in shopping centres (at least during the summer). 2) Shopping centres are located above MTR stations and bus interchanges, and below people's houses. Most people go to work using public transportation, so they go through the shopping centres owned by Link (and of course all the other Reits) daily. This means constant traffic, and sales. Of course I can see a change in the shops in HK malls. For example, the shops selling gold jewellery and beauty products to Chinese tourists will gradually disappear (I don't know why they are still open in the shopping centre near my house), but they will be replaced by other shops selling stuff for HK people. Though the rent will be lower, I don't see many vacancies in HK shopping centres (there are some in a shopping centre near my house, but it should be filled easily if the owners agree to cut the rent). Since Link owns predominantly shopping centres for HK working class people, I don't see much of a change in the number of shoppers (and profits) in the future. I can see a drop in Australian and Chinese shopping centres (and income from car parks). Perhaps someone can tell us how much of the total income to Reit comes from these sources?
I believe both SPG and Link are rather safe investments, at present day prices, for dividend investors. Although SPG might drop more if the virus doesn't go away/there isn't a vaccine and malls are closed again, and Link will drop more if the PLA sends its tanks.
Full disclosure, I own both SPG and Link.