It's possible for two things to be true at once. The new rules can be moderately bad for big companies and cause them to do layoffs and also cause them to be catastrophically bad for startups, giving incumbent big tech companies another relative advantage over them.

This is also ignoring the short-term vs. long-term effects. In the first year the incumbent companies are in the same boat as the new ones because they already deducted all their R&D expenses from the previous year when they were still allowed to, so they get a minimal deduction this year and have no advantage. But five years from now, they'll have five years worth of R&D they're still amortizing -- notably, this means the government is no longer getting more revenue from them in the current year than they would otherwise, since their average R&D expense and their average amortized deduction are now equal -- whereas the startup has no historical R&D to deduct and is put at a disadvantage.